Display device and electronic device

ABSTRACT

A novel display device capable of adjusting color purity is provided. A novel display device with improved adhesion of a color filter is provided. A novel display device capable of excellent reflective display is provided. The display device includes a transistor, a reflective electrode layer formed on the same surface as a source electrode layer or a drain electrode layer of the transistor, a first insulating layer over the reflective electrode layer, a coloring layer which is over the first insulating layer and overlaps with the reflective electrode layer, a second insulating layer over the coloring layer, and a pixel electrode layer over the second insulating layer. The coloring layer includes at least a first opening and a second opening. The pixel electrode layer is electrically connected to the transistor through the first opening. The second insulating layer is in contact with the first insulating layer in the second opening.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an object, a method, or a manufacturingmethod. In addition, the present invention relates to a process, amachine, manufacture, or a composition of matter. One embodiment of thepresent invention relates to a semiconductor device, a display device,an electronic device, a manufacturing method thereof, or a drivingmethod thereof. One embodiment of the present invention particularlyrelates to, for example, a reflective liquid crystal display device.

Note that the term “display device” means a device including a displayelement. In addition, the display device includes a driver circuit fordriving a plurality of pixels, and the like. Furthermore, the displaydevice may include a control circuit, a power supply circuit, a signalgeneration circuit, or the like formed over another substrate.

2. Description of the Related Art

With the recent rapid spread of portable information terminals such assmartphones, improvement in their performance has progressed rapidly.Their screens have been increased in size and resolution, and somerecent ones have resolutions as high as over 300 ppi.

For example, liquid crystal display devices generally have a structurein which R, G, and B sub-pixels are provided in a display region andprovided with their respective color filters. The color filters areprovided over a substrate (a counter substrate) which faces anactive-matrix substrate (a substrate provided with elements (e.g.,transistors) for driving pixels).

With the increase in resolution, the alignment accuracy between anactive-matrix substrate and a counter substrate provided with colorfilters can be recognized as a problem. In view of this problem,attention has been focused on what is called a color filter on array(COA) structure, in which a color filter is formed on the active-matrixsubstrate side.

As a liquid crystal display device with a COA structure, a reflective orsemi-transmissive liquid crystal display device which includes a colorfilter, a pixel electrode, and a reflective layer on the active-matrixsubstrate side and in which light entering from the counter substrateside is transmitted through the pixel electrode and the color filter andis reflected by the underlying reflective layer and is visuallyrecognized is disclosed (e.g., see Patent Document 1 and Patent Document2).

PATENT DOCUMENTS [Patent Document 1] Japanese Published PatentApplication No. 2000-187209 [Patent Document 2] PCT InternationalPublication No. 2011/045953 SUMMARY OF THE INVENTION

In the case of a reflective display device in which a counter substrateis provided with a color filter, light such as external light istransmitted through the color filter, reflected by a reflective film orthe like, and transmitted through the color filter again.

Also in the case of a reflective display device having a COA structure,light such as external light is transmitted through the color filter,reflected by a reflective film or the like, and transmitted through thecolor filter again. That is, light such as external light is transmittedthrough the color filter twice and is then observed by a viewer. Thismay increase the color purity of reflected light. In the case whereexternal light is relatively weak in a room or the like, reflected lightwith high color purity is weak, resulting in dark display.

The color purity of reflected light in a reflective display device canbe adjusted by the thickness of a color filter, for example. The colorpurity can be adjusted also by changing a coloring material, such as apigment, which is used for the color filter. However, when the thicknessof the color filter is large or small, it is difficult to make thethickness uniform all over a substrate surface. In the case where acoloring material used for the color filter is changed, the materialchange results in increases in development time and cost.

Another problem is low adhesion between the color filter and a surfaceover which the color filter is formed. For example, as the color filter,a photosensitive resin film is formed by applying and drying aphotosensitive resin solution in which a coloring material is dispersed.Since the coloring material is dispersed, light intensity at the time oflight exposure of the photosensitive resin film decreases in a depthdirection, which may cause insufficient photocuring and low adhesion ator around the interface between the photosensitive resin film and thesurface over which the photosensitive resin film is formed.

In view of the above problems, an object of one embodiment of thepresent invention is to provide a novel display device capable ofadjusting color purity. Another object of one embodiment of the presentinvention is to provide a novel display device with improved adhesion ofa color filter. Another object of one embodiment of the presentinvention is to provide a novel display device of which productivity isimproved. Another object of one embodiment of the present invention isto provide a novel display device capable of excellent reflectivedisplay. Another object of one embodiment of the present invention is toprovide a novel display device with a COA structure that is capable ofexcellent reflective display. Another object of one embodiment of thepresent invention is to provide a novel display device or the like.

Note that the descriptions of these objects do not disturb the existenceof other objects. Note that in one embodiment of the present invention,there is no need to achieve all the objects. Note that other objectswill be apparent from the description of the specification, thedrawings, the claims, and the like and other objects can be derived fromthe description of the specification, the drawings, the claims, and thelike.

One embodiment of the present invention is a display device whichincludes a pixel region, a transistor formed in the pixel region, asource electrode layer or a drain electrode layer of the transistor, aninsulating layer over the source electrode layer or the drain electrodelayer, a pixel electrode layer over the insulating layer, and a coloringlayer overlapping with the pixel electrode layer and the drain electrodelayer. The pixel electrode layer is electrically connected to thetransistor. The coloring layer includes at least a first opening and asecond opening.

In the above embodiment, the coloring layer may be formed over a countersubstrate, and a substrate provided with the pixel electrode layer andthe counter substrate may be aligned with and attached to each othersuch that the coloring layer overlaps with the pixel electrode layer. Inthe above embodiment, the pixel electrode layer may function as areflective electrode layer.

In the above embodiment, the coloring layer may be a material layercapable of transmitting light in a red wavelength range, a materiallayer capable of transmitting light in a green wavelength range, or amaterial layer capable of transmitting light in a blue wavelength range.As another color of the coloring layer, cyan, magenta, yellow, or thelike may be used. In the case where three or more kinds of coloringlayers are used to achieve full-color display, each coloring layer mayhave an upper surface shape different from those of the coloring layersof the other colors, and for example, may have a different openingshape. A plurality of coloring layers are not necessarily formed overone substrate, and for example, the counter substrate may be providedwith a first coloring layer and the substrate provided with thetransistor may be provided with a second coloring layer and a thirdcoloring layer.

In the above embodiment, the display device may further include a secondcoloring layer and a third coloring layer. The second coloring layerincludes at least a third opening and a fourth opening. Upper surfaceshapes of the third opening and the fourth opening are different fromthose of the first opening and the second opening. When an opening in ared coloring layer has a larger area than that of an opening in a bluecoloring layer, reflectance can be improved with an NTSC ratiomaintained.

Another embodiment of the present invention is a display device whichincludes a pixel region, a transistor formed in the pixel region, areflective electrode layer formed on the same surface as a sourceelectrode layer or a drain electrode layer of the transistor, a firstinsulating layer over the reflective electrode layer, a coloring layerwhich is over the first insulating layer and overlaps with thereflective electrode layer, a second insulating layer over the coloringlayer, and a pixel electrode layer over the second insulating layer. Thecoloring layer includes at least a first opening and a second opening.The pixel electrode layer is electrically connected to the transistorthrough the first opening. The second insulating layer is in contactwith the first insulating layer in the second opening.

Another embodiment of the present invention is a display device whichincludes a pixel region, a transistor formed in the pixel region, areflective electrode layer formed on the same surface as a sourceelectrode layer or a drain electrode layer of the transistor, a firstinsulating layer including an inorganic insulating material over thereflective electrode layer, a coloring layer which is over the firstinsulating layer and overlaps with the reflective electrode layer, asecond insulating layer including an organic insulating material overthe coloring layer, and a pixel electrode layer over the secondinsulating layer. The coloring layer includes at least a first openingand a second opening. The pixel electrode layer is electricallyconnected to the transistor through the first opening. The secondinsulating layer is in contact with the first insulating layer in thesecond opening.

In each of the above embodiments, it is preferable that the transistorinclude a gate electrode layer, a gate insulating layer over the gateelectrode layer, a semiconductor layer over the gate insulating layer,and the source electrode layer and the drain electrode layer which arein contact with the gate insulating layer and the semiconductor layer.

In each of the above embodiments, it is preferable that the firstinsulating layer include a third opening overlapping with the firstopening and the pixel electrode layer be electrically connected to thedrain electrode layer of the transistor through the first opening andthe third opening.

In each of the above embodiments, it is preferable that thesemiconductor layer be an oxide semiconductor layer. The oxidesemiconductor layer preferably includes an oxide represented by anIn-M-Zn oxide that contains at least indium (In), zinc (Zn), and M (Mrepresents Al, Ga, Ge, Y, Zr, Sn, La, Ce, or Hf).

In each of the above embodiments, a touch panel may overlap with thepixel region, or the counter substrate may be provided with a circuithaving a touch input function.

Embodiments of the present invention also include an electronic deviceincluding the above display device.

In one embodiment of the present invention, a novel display devicecapable of adjusting color purity can be provided. In one embodiment ofthe present invention, a novel display device with improved adhesion ofa color filter can be provided. Furthermore, in one embodiment of thepresent invention, a novel display device of which productivity isimproved can be provided. Furthermore, in one embodiment of the presentinvention, a novel display device capable of excellent reflectivedisplay can be provided. Furthermore, in one embodiment of the presentinvention, a novel display device or the like can be provided.

Note that the descriptions of these effects do not disturb the existenceof other effects. Note that in one embodiment of the present invention,there is no need to achieve all the effects. Note that other effectswill be apparent from the description of the specification, thedrawings, the claims, and the like and other effects can be derived fromthe description of the specification, the drawings, the claims, and thelike.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 illustrates a top view of a display device;

FIGS. 2A to 2C each illustrate a top view of a coloring layer of adisplay device:

FIGS. 3A and 3B illustrate cross-sectional views of a display device;

FIGS. 4A to 4D are cross-sectional views illustrating a method formanufacturing a display device;

FIGS. 5A to 5D are cross-sectional views illustrating a method formanufacturing a display device;

FIGS. 6A to 6C are cross-sectional views illustrating a method formanufacturing a display device:

FIGS. 7A and 7B illustrate a cross section of a display device and amethod for manufacturing the display device;

FIGS. 8A and 8B are a block diagram of a display device and a circuitdiagram of a pixel;

FIG. 9 illustrates a display module:

FIGS. 10A to 10H each illustrate an electronic device;

FIGS. 11A to 11C show optical micrographs in an example:

FIG. 12 shows a cross-sectional TEM image in an example:

FIGS. 13A and 13B show cross-sectional TEM images in an example;

FIGS. 14A to 14C each illustrate a top view of a coloring layer of adisplay device;

FIG. 15 is a cross-sectional view illustrating a method formanufacturing a display device:

FIGS. 16A and 16B each illustrate a cross-sectional view of a displaydevice:

FIGS. 17A and 17B each illustrate a cross-sectional view of a displaydevice:

FIGS. 18A and 18B each illustrate a cross-sectional view of a displaydevice:

FIGS. 19A and 19B each illustrate a cross-sectional view of a displaydevice;

FIGS. 20A and 20B each illustrate a cross-sectional view of a displaydevice;

FIG. 21 illustrates a top view of a display device:

FIGS. 22A and 22B each illustrate a top view of a coloring layer of adisplay device;

FIGS. 23A and 23B each illustrate a cross-sectional view of a displaydevice:

FIGS. 24A and 24B are a diagram illustrating a method for measuringreflectance and a graph showing reflectance;

FIGS. 25A and 25B show a photograph of a display device andcharacteristics of the display device;

FIG. 26 is a schematic cross-sectional view of a display device:

FIGS. 27A and 27B are conceptual diagrams each illustrating an exampleof a driving method of a display device; and

FIG. 28 is a graph showing changes in images caused by a refreshoperation.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be hereinafter described with reference to drawings.However, the embodiments can be implemented with various modes. It willbe readily appreciated by those skilled in the art that modes anddetails can be changed in various ways without departing from the spiritand scope of the present invention. Therefore, the present inventionshould not be construed as being limited to the description in thefollowing embodiments.

In drawings, the size, the layer thickness, or the region is exaggeratedfor clarity in some cases. Therefore, embodiments of the presentinvention are not limited to such a scale. Note that drawings areschematic views showing ideal examples, and embodiments of the presentinvention are not limited to shapes or values shown in the drawings.

Ordinal numbers such as “first”, “second”, and “third” in thisspecification are used in order to avoid confusion among components, andthe terms do not limit the components numerically.

Note that in this specification, terms for describing arrangement, suchas “over” and “under”, are used for convenience for describing thepositional relation between components with reference to drawings.Further, the positional relation between components is changed asappropriate in accordance with a direction in which each component isdescribed. Thus, the positional relation is not limited to thatdescribed with a term used in this specification and can be explainedwith another term as appropriate depending on the situation.

In this specification and the like, a transistor is an element having atleast three terminals of a gate, a drain, and a source. In addition, thetransistor has a channel region between a drain (a drain terminal, adrain region, or a drain electrode layer) and a source (a sourceterminal, a source region, or a source electrode layer), and current canflow through the drain, the channel region, and the source.

Functions of a “source” and a “drain” are sometimes replaced with eachother when a transistor of opposite polarity is used or when thedirection of current flowing is changed in circuit operation, forexample. Therefore, the terms “source” and “drain” can be replaced witheach other in this specification and the like.

In this specification and the like, the term “electrically connected”includes the case where components are connected through an objecthaving any electric function. There is no particular limitation on an“object having any electric function” as long as electric signals can betransmitted and received between components that are connected throughthe object. Examples of an “object having any electric function” includea switching element such as a transistor, a resistor, an inductor, acapacitor, and an element with a variety of functions, as well as anelectrode and a wiring.

In this specification and the like, a pixel region includes at least apixel (corresponding to a display unit that can control the luminance ofone color element (e.g., any one of R (red), G (green), and B (blue))).Therefore, in a color display device, the minimum display unit of acolor image is composed of three pixels of an R pixel, a G pixel, and aB pixel. Note that the colors of the color elements for displaying colorimages are not limited to three colors, and may be more than threecolors or may include a color other than R, G, and B. For example, adisplay unit may be composed of four pixels of the R pixel, the G pixel,the B pixel, and a W (white) pixel. Alternatively, a display unit may becomposed of a plurality of color elements among R, G, and B as inPenTile layout.

Embodiment 1

In this embodiment, a display device of one embodiment of the presentinvention will be described with reference to FIG. 1, FIGS. 2A to 2C,FIGS. 3A and 3B, FIGS. 4A to 4D. FIGS. 5A to 5D, and FIGS. 6A to 6C.

FIG. 1 illustrates a top view of an example of a display device of oneembodiment of the present invention. In the top view of FIG. 1, whichshows some pixel regions (three pixels) in the display device,components such as a gate insulating layer are partly omitted to avoidcomplexity.

In FIG. 1, a transistor 150 includes a conductive layer 104 a serving asa gate electrode layer, a gate insulating layer (not illustrated in FIG.1), a semiconductor layer 108 where a channel region is formed, aconductive layer 110 b_1 serving as a source electrode layer, and aconductive layer 10 b_2 serving as a drain electrode layer. A gate line104 including the conductive layer 104 a serving as the gate electrodelayer of the transistor 150 extends in the horizontal direction, and asource line 110 including the conductive layer 110 b_1 serving as thesource electrode layer of the transistor 150 extends in the verticaldirection. A pixel region 120 is formed in a region defined by two gatelines 104 adjacent to each other and two source lines 110 adjacent toeach other. In this manner, the transistor 150 is formed in the pixelregion 120.

Furthermore, a conductive layer 104 b that is formed in the same step asthe conductive layer 104 a serving as a gate electrode layer and theconductive layer 110 b_2 that serves as a drain electrode layer arestacked with an insulating layer that is formed in the same step as thegate insulating layer positioned therebetween. The conductive layer 104b, the insulating layer that is formed in the same step as the gateinsulating layer, and the conductive layer 110 b_2 form a capacitor 152.

The transistor 150 is electrically connected to a pixel electrode layer118. Specifically, the pixel electrode layer 118 is electricallyconnected to the conductive layer 110 b_2 that serves as the drainelectrode layer of the transistor 150, through an opening 134 and anopening 138.

It is preferable that the area of a region where the source line 110including the conductive layer 110 b_1 and the gate line 104 includingthe conductive layer 104 a intersect with each other be small asillustrated in FIG. 1. Reducing the area of the source line 110 and thearea of the gate line 104 can reduce parasitic capacitance that can begenerated between the source line 110 and the gate line 104.

The pixel region 120 includes a conductive layer 110 b_3 that is formedin the same step as the conductive layer 110 b_1 serving as the sourceelectrode layer of the transistor 150 and the conductive layer 110 b_2serving as the drain electrode layer of the transistor 150. Note thatthe conductive layer 110 b_3 has a function of a reflective electrodelayer. The conductive layer 110 b_3 overlaps with a coloring layer 114.The coloring layer 114 overlaps with the pixel electrode layer 118.

In the structure in FIG. 1, light (mainly external light) that isincident on the conductive layer 110 b_3 is transmitted through at leastthe pixel electrode layer 118 and the coloring layer 114 and isreflected by the conductive layer 110 b_3. In other words, the displaydevice in this embodiment performs color display with the use of lightreflected by the conductive layer 110 b_3 serving as a reflectiveelectrode layer. Note that the conductive layer 110 b_3 has a functionof a capacitor line. The conductive layer 110 b_3 is connected to thatin an adjacent pixel.

The coloring layer 114 has an opening 134 serving as a first opening andan opening 136 serving as a second opening. Note that FIG. 1 illustratesa structure in which one pixel is provided with 16 openings 136.However, the shape or number of openings 136 is not limited to thisexample.

The opening 134 serves as an opening for connection between thetransistor 150 and the pixel electrode layer 118. The opening 136 has afunction of adjusting the color purity of the coloring layer 114. Inother words, the color purity of the coloring layer 114 can be adjustedwith the shape or number of openings 136.

Such a structure in which the coloring layer 114 has the opening 136makes it easy to adjust the color purity of the coloring layer 114.

Here, an upper surface shape of the coloring layer 114 in the displaydevice illustrated in FIG. 1 is described more specifically. FIG. 2A isa top view of the coloring layer 114. Note that in FIG. 2A, componentsother than the coloring layer 114 are omitted. In addition, FIG. 2Acorresponds to a top view of one pixel.

The coloring layer 114 illustrated in FIG. 2A has the opening 134 andthe openings 136. In FIG. 2A, a region overlapping with the coloringlayer 114 of an adjacent pixel, here the coloring layer 114 of an upperadjacent pixel, is denoted by a region 141, and a region overlappingwith the coloring layer 114 of a lower adjacent pixel is denoted by aregion 142. Such an arrangement in which one pixel overlaps with part ofthe coloring layer 114 of an adjacent pixel can suppress lightreflection by the gate line 104 or the source line 110. In other words,when the coloring layer 114 of an adjacent pixel is stacked, part of thecoloring layer 114 can function as a so-called black matrix (BM).

Note that FIG. 2A illustrates, as an example, a structure in which thecoloring layers 114 of adjacent pixels on both sides separately overlapwith the coloring layer 114; however, the present invention is notlimited to this structure. For example, each of the coloring layers 114of the adjacent pixels may overlap with the coloring layer 114. Notethat in the case where each of the coloring layers 114 of the adjacentpixels overlaps with the coloring layer 114, surface unevenness in thepixel region 120 or around the pixel region 120 may increase. In view ofthe flatness in the pixel region 120 or around the pixel region 120, itis preferable that the coloring layers 114 of both the adjacent pixelsseparately overlap with the coloring layer 114 as illustrated in FIG.2A. Alternatively, a black coloring layer serving as a black matrix (BM)may be provided around the pixel region 120.

FIGS. 2B and 2C illustrate modification examples of the coloring layer114 in FIG. 2A.

The coloring layer 114 in FIG. 2B differs from the coloring layer 114 inFIG. 2A in the shape of the opening 134 and the shape and arrangement ofthe openings 136. The coloring layer 114 in FIG. 2C differs from thecoloring layer 114 in FIG. 2A in the shape of the opening 134 and theshape and arrangement of the openings 136. In this manner, the shapes,numbers, or arrangement of the opening 134 and the openings 136 of thecoloring layer 114 can be variously changed to adjust the color purityof the coloring layer 114. Although the openings 136 illustrated in FIG.1 and FIGS. 2A to 2C have quadrilateral shapes, the present invention isnot limited to these examples and the openings 136 may have a circularshape, an elliptical shape, or the like.

Note that the shape and arrangement of the coloring layer 114, theopening 134, the openings 136, and the like may be changed depending onthe color of the pixel. For example, the structure in FIG. 2A may beadopted for an R pixel; the structure in FIG. 2B may be adopted for a Gpixel; and the structure in FIG. 2C may be adopted for a B pixel. For aW pixel, a structure not provided with the coloring layer 114 may beadopted, or the opening 134 or the openings 136 may be larger than thosein pixels of other colors.

Alternatively, a transmissive region 401 may be provided in one pixel.Alternatively, a semi-transmissive display device including thetransmissive region 401 and a reflective region 400 may be formed. FIGS.14A to 14C illustrate examples in which the upper surface shapes of thecoloring layers 114 in FIGS. 2A to 2C are used in semi-transmissivedisplay devices. As illustrated in FIGS. 14A to 14C, it is possible thatthe opening 136 is not provided in the transmissive region 401.

Next, cross sections of the display device illustrated in FIG. 1 aredescribed with reference to FIGS. 3A and 3B. Note that FIG. 3A is across-sectional view corresponding to a cross section taken alongdashed-dotted line X1-Y1 in FIG. 1. FIG. 3B is a cross-sectional viewcorresponding to a cross section taken along dashed-dotted line X2-Y2 inFIG. 1.

The display device in FIG. 3A includes a first substrate 102; theconductive layer 104 a serving as a gate electrode layer over the firstsubstrate 102; the conductive layer 104 b formed in the same step as theconductive layer 104 a; an insulating layer 106 a and an insulatinglayer 106 b over the first substrate 102 and the conductive layers 104 aand 104 b; the semiconductor layer 108 which is over the insulatinglayer 106 b and overlaps with the conductive layer 104 a; a conductivelayer 110 a_1 serving as a source electrode layer over the semiconductorlayer 108 and the insulating layer 106 b; a conductive layer 110 a_2serving as a drain electrode layer over the semiconductor layer 108 andthe insulating layer 106 b; a conductive layer 110 a_3 formed in thesame step as the conductive layers 110 a_1 and 110 a_2; the conductivelayers 110 b_1, 110 b_2, and 110 b_3 over the conductive layers 110 a_1,110 a_2, and 110 a_3; a conductive layer 110 c_1 over the conductivelayer 110 b_2; an insulating layer 112 serving as a protectiveinsulating film over the insulating layer 106 b, the semiconductor layer108, and the conductive layers 110 b_1, 110 b_2, 110 b_3, and 110 c_1;the coloring layer 114 having a function of a color filter over theinsulating layer 112; an insulating layer 116 having a function of anovercoat layer over the coloring layer 114; the pixel electrode layer118 over the insulating layer 116; a liquid crystal layer 166 over thepixel electrode layer 118; a conductive layer 164 having a function of acounter electrode over the liquid crystal layer 166; and a secondsubstrate 162 over the conductive layer 164.

Note that the conductive layer 104 a, the insulating layers 106 a and106 b, the semiconductor layer 108, and the conductive layers 110 a_1,110 a 2, 110 b_1, and 110 b_2 form the transistor 150. The conductivelayer 104 b, the insulating layers 106 a and 106 b, and the conductivelayers 110 a_3 and 110 b_3 form the capacitor 152.

Note that a portion of the insulating layers 106 a and 106 b whichoverlaps with the conductive layer 104 a serving as a gate electrodelayer has a function of a gate insulating layer of the transistor 150,and a portion thereof which overlaps with the conductive layer 104 b hasa function of a dielectric layer of the capacitor 152.

The insulating layers 106 a and 106 b are provided with an opening 132which reaches the conductive layer 104 b, and the conductive layers 110a_2 and 110 b_2 having a function of a drain electrode layer of thetransistor 150 are connected to the conductive layer 104 b through theopening 132.

Note that the example in which the opening 132 is provided is describedhere; however, one embodiment of the present invention is not limited tothis example. For example, a structure in which the opening is notprovided as illustrated in FIG. 16A may be employed. In that case, theconductive layer 110 b_3 is included in the same island as theconductive layer 110 b_2. Similarly, the conductive layer 110 a_3 isincluded in the same island as the conductive layer 110 a_2. Theconductive layer 104 b can serve as a capacitor line. Accordingly, insuch a case, the conductive layer 104 b is preferably provided so as toextend in a direction substantially parallel to the conductive layer 104a or the gate line 104.

The coloring layer 114 is provided with the opening 134 and the openings136. In other words, the insulating layer 116 over the coloring layer114 is in contact with the insulating layer 112 in the opening 134. Notethat the adhesion of the insulating layer 116 to the insulating layer112 is higher than that of the coloring layer 114. Therefore, when thereis a region where the insulating layer 116 and the insulating layer 112are in contact with each other, separation of the coloring layer 114 canbe suppressed even in the case where the adhesion between the coloringlayer 114 and the insulating layer 112 is not sufficient.

The insulating layer 112 is preferably formed with an inorganicinsulating material. The insulating layer 116 is preferably formed withan organic insulating material. When the insulating layer 112 is formedwith an inorganic insulating material, the insulating layer 112 can havefavorable characteristics of the interface with the semiconductor layer108. When the insulating layer 116 is formed with an organic insulatingmaterial, the pixel electrode layer 118 formed over the insulating layer116 can have high flatness.

The color purity of the coloring layer 114 can be adjusted with theopenings 136 provided in the coloring layer 114. For example, the colorpurity of the coloring layer 114 can be adjusted by adjusting the shapeof the openings 136 or the area of the openings 136.

With such a structure in which the coloring layer 114 has the openings136, a novel display device capable of adjusting color purity can beprovided. It addition, a novel display device with improved adhesion ofthe coloring layer 114 used as a color filter can be provided.

The insulating layer 112 is provided with the opening 138. The pixelelectrode layer 118 is connected to the conductive layer 110 c_1 servingas a drain electrode layer of the transistor 150, through the openings134 and 138.

The conductive layer 110 b_3 has a function of a reflective electrodelayer. Therefore, a highly reflective conductive layer is preferablyused. For example, the highly reflective conductive layer is formed tohave a single-layer structure or a stacked-layer structure including anyof metals such as aluminum, silver, palladium, and copper or an alloycontaining any of these metals as its main component. It is particularlypreferable to use a material including aluminum for the conductive layer110 b_3 in terms of cost, processability, and the like. As theconductive layer 110 c_1, it is preferable to use a highlyoxidation-resistant conductive layer. When a highly oxidation-resistantconductive layer is used as the conductive layer 110 c_1, its contactresistance with the pixel electrode layer 118 can be decreased. This canincrease reflectance and decrease contact resistance with the pixelelectrode layer.

In other words, in the display device illustrated in FIG. 3A, the highlyreflective conductive layer is used in the reflective region, and thehighly oxidation-resistant conductive layer is used in a region forcontact with the pixel electrode layer; thus, the display device is anovel display device which is capable of excellent reflective displayand in which contact failures between a transistor and a pixel electrodelayer are reduced.

Note that the transmissive region 401 may be provided as illustrated inFIG. 16B.

In the display device in FIG. 3A, the liquid crystal layer 166 isprovided between the first substrate 102 and the second substrate 162which faces the first substrate 102.

The conductive layer 164 is formed under the second substrate 162. Thepixel electrode layer 118, the liquid crystal layer 166, and theconductive layer 164 form a liquid crystal element 170. By applicationof voltage between the pixel electrode layer 118 and the conductivelayer 164, the alignment state in the liquid crystal layer 166 can becontrolled. In FIG. 3A, the pixel electrode layer 118 and the conductivelayer 164 are in contact with the liquid crystal layer 166; however, oneembodiment of the present invention is not limited to this structure.For example, alignment films may be formed in a region where the pixelelectrode layer 118 is in contact with the liquid crystal layer 166 anda region where the conductive layer 164 is in contact with the liquidcrystal layer 166.

In the display device in FIG. 3A, the conductive layer 110 b_3 servingas a reflective electrode layer, the coloring layer 114, and the pixelelectrode layer 118 can be formed over the first substrate 102; thus, ascompared with the case where the coloring layer is formed on the secondsubstrate 162 side, high alignment accuracy can be achieved. With thisstructure, even a liquid crystal display device with high resolution(e.g., 300 ppi or more) can be a reflective liquid crystal displaydevice capable of color display.

Note that the transistor 150 may be provided with a gate electrode overa channel or under the channel, or may be provided with gate electrodesover and under the channel. FIG. 17A illustrates an example including aconductive layer 118 a which is formed at the same time as the pixelelectrode layer 118. The conductive layer 118 a can serves as a gateelectrode of the transistor 150. Note that the conductive layer 118 amay be connected to the conductive layer 104 a. In that case, the samesignal or potential is supplied to the conductive layer 118 a and theconductive layer 104 a. Alternatively, different signals or potentialsmay be supplied to the conductive layer 118 a and the conductive layer104 a. Since the conductive layer 18 a is formed at the same time as thepixel electrode layer 118 through the same film formation step and thesame etching step, an increase in the number of steps in the process canbe prevented. Note that one embodiment of the present invention is notlimited to this example. For example, a different conductive layer maybe used to form a conductive layer having a function of a gate electrodeof the transistor 150. FIGS. 17B and 18A illustrate examples of such acase. Conductive layers 199 and 199 a may contain a material used forthe conductive layer 110 c_1. Alternatively, the conductive layers 199and 199 a may contain a material similar to the above-describedmaterials that can be used for the conductive layers 104 a, 110 a_1, 110b_1, and 110 c_1, and the like.

Note that as illustrated in FIG. 18B, a conductive layer 199 b may beprovided as a conductive layer which is formed at the same time as theconductive layer 199 a through the same film formation step and the sameetching step. This conductive layer can serve as a reflective electrodewhen formed using a highly reflective material similar to that used forthe conductive layer 110 b_3. Alternatively, the conductive layer canform a capacitor when overlapping with the conductive layer 110 b_2. Inthat case, the conductive layer 199 b may be connected to the conductivelayer 104 b.

Note that a conductive layer 199 c may be provided as a conductive layerwhich is formed at the same time as the conductive layer 199 a throughthe same film formation step and the same etching step. The conductivelayer 199 c may be provided in a portion for connection to the pixelelectrode layer 118. FIGS. 19A and 19B illustrate examples of such acase. In that case, the conductive layer 199 a may contain a materialsimilar to that of the conductive layer 110 c_1. Note that theconductive layer 199 a is not necessarily provided. FIGS. 20A and 20Billustrate examples of such a case.

Next, the display device illustrated in FIG. 3B will be described below.

The display device in FIG. 3B includes the first substrate 102; the gateline 104 over the first substrate 102; the insulating layers 106 a and106 b over the gate line 104; conductive layers 110 a_4 and 110 b_4 overthe insulating layer 106 b; the insulating layer 112 over the insulatinglayer 106 b and the conductive layer 110 b_4; the coloring layer 114over the insulating layer 112; coloring layers 114 a and 114 b over thecoloring layer 114; the insulating layer 116 over the coloring layers114, 114 a, and 114 b; the liquid crystal layer 166 over the insulatinglayer 116; the conductive layer 164 over the liquid crystal layer 166;and the second substrate 162 over the conductive layer 164. Note thatthe conductive layers 110 a 4 and 110 b 4 serve as the source line 110.

FIG. 3B is a cross-sectional view of a region where the gate line 104and the conductive layers 110 a_4 and 110 b_4 serving as the source line110 intersect with each other.

When the coloring layers 114 a and 114 b are formed over the coloringlayer 114 as illustrated in FIG. 3B, surface reflection due to the gateline 104 or the conductive layer 110 b_4 can be suppressed. Note thatthe coloring layer 114 a is a coloring layer of an adjacent pixel, herethe lower pixel in FIG. 1. The coloring layer 114 b is a coloring layerof an adjacent pixel, here the upper pixel in FIG. 1. For example, thecoloring layer 114 may be green (G); the coloring layer 114 a may beblue (B); and the coloring layer 114 b may be red (R).

With such a structure in which coloring layers are stacked in a regionother than at least a reflective region, i.e., a structure in which acoloring layer overlaps with a coloring layer of an adjacent pixel, partof the coloring layers can function as a black matrix.

Note that other components of the display device in FIG. 1 and FIGS. 3Aand 3B are described in detail in Method for Manufacturing DisplayDevice.

<Method for Manufacturing Display Device>

A method for manufacturing the display device illustrated in FIG. 1 andFIGS. 3A and 3B is described below with reference to FIGS. 4A to 4D,FIGS. 5A to 5D, and FIGS. 6A to 6C.

First, the first substrate 102 is prepared. For the first substrate 102,a glass material such as aluminosilicate glass, aluminoborosilicateglass, or barium borosilicate glass is used. In the mass production, forthe first substrate 102, a mother glass with any of the following sizesis preferably used: the 8th generation (2160 mm×2460 mm), the 9thgeneration (2400 mm×2800 mm, or 2450 mm×3050 mm), the 10th generation(2950 mm×3400 mm), and the like. High process temperature and a longperiod of process time drastically shrink the mother glass. Thus, in thecase where mass production is performed with the use of the motherglass, the heating temperature in the manufacturing process ispreferably 600° C. or lower, further preferably 450° C. or lower, stillfurther preferably 350° C. or lower.

Then, a conductive layer is formed over the first substrate 102 andprocessed into desired shapes, so that the conductive layers 104 a and104 b are formed (see FIG. 4A).

For the conductive layers 104 a and 104 b, a metal element selected fromaluminum, chromium, copper, tantalum, titanium, molybdenum, andtungsten, an alloy containing any of these metal elements as acomponent, an alloy containing these metal elements in combination, orthe like can be used. In addition, the conductive layers 104 a and 104 bmay have a single-layer structure or a stacked-layer structure of two ormore layers. For example, a two-layer structure in which a titanium filmis stacked over an aluminum film, a two-layer structure in which atitanium film is stacked over a titanium nitride film, a two-layerstructure in which a tungsten film is stacked over a titanium nitridefilm, a two-layer structure in which a tungsten film is stacked over atantalum nitride film or a tungsten nitride film, a three-layerstructure in which a titanium film, an aluminum film, and a titaniumfilm are stacked in this order, and the like can be given.Alternatively, an alloy film or a nitride film in which aluminum and oneor more elements selected from titanium, tantalum, tungsten, molybdenum,chromium, neodymium, and scandium are contained may be used. Theconductive layers 104 a and 104 b can be formed by a sputtering method,for example.

Next, the insulating layers 106 a and 106 b are formed over the firstsubstrate 102 and the conductive layers 104 a and 104 b (see FIG. 4B).

The insulating layer 106 a is formed to have a single-layer structure ora stacked-layer structure using, for example, any of a silicon nitrideoxide film, a silicon nitride film, an aluminum oxide film, and the likewith a PE-CVD apparatus. In the case where the insulating layer 106 ahas a stacked-layer structure, it is preferable that a silicon nitridefilm with fewer defects be provided as a first silicon nitride film, anda silicon nitride film from which hydrogen and ammonia are less likelyto be released be provided over the first silicon nitride film, as asecond silicon nitride film. As a result, hydrogen and nitrogencontained in the insulating layer 106 a can be prevented from moving ordiffusing into the semiconductor layer 108 formed later.

The insulating layer 106 b is formed to have a single-layer structure ora stacked-layer structure using any of a silicon oxide film, a siliconoxynitride film, and the like with a PE-CVD apparatus.

As for the insulating layers 106 a and 106 b, for example, a400-nm-thick silicon nitride film can be formed as the insulating layer106 a, and then a 50-nm-thick silicon oxynitride film can be formed asthe insulating layer 106 b. The silicon nitride film and the siliconoxynitride film are preferably formed in succession in a vacuum suchthat fewer impurities are mixed into the films. Note that portions ofthe insulating layers 106 a and 106 b overlapping with the conductivelayer 104 a serve as the gate insulating layer of the transistor 150. Inaddition, portions of the insulating layers 106 a and 106 b overlappingwith the conductive layer 104 b serve as a dielectric layer of thecapacitor 152.

Note that silicon nitride oxide refers to an insulating material thatcontains more nitrogen than oxygen, whereas silicon oxynitride refers toan insulating material that contains more oxygen than nitrogen.

When the gate insulating layer has the above structure, the followingeffects can be obtained, for example. The silicon nitride film has ahigher relative permittivity than a silicon oxide film and needs alarger thickness for an equivalent capacitance. Thus, the physicalthickness of the gate insulating layer can be increased. This makes itpossible to reduce a decrease in the withstand voltage of the transistor150 and furthermore increase the withstand voltage, thereby preventingelectrostatic breakdown of the transistor 150.

Next, a semiconductor layer is formed over the insulating layer 106 band processed into a desired shape, so that the semiconductor layer 108is formed. Note that the semiconductor layer 108 is formed in a positionoverlapping with the conductive layer 104 a (see FIG. 4C).

For the semiconductor layer 108, amorphous silicon, polycrystallinesilicon, single crystal silicon, or the like can be used, for example.It is particularly preferable to use an oxide semiconductor for thesemiconductor layer 108. The oxide semiconductor preferably includes anoxide represented by an In-M-Zn oxide that contains at least indium(In), zinc (Zn), and M (M represents Al, Ga, Ge, Y, Zr, Sn, La, Ce, orHf). Alternatively, both In and Zn are preferably contained.

As the oxide semiconductor, for example, any of the following can beused: indium oxide, tin oxide, zinc oxide, an In—Zn oxide, a Sn—Znoxide, an Al—Zn oxide, a Zn—Mg oxide, a Sn—Mg oxide, an In—Mg oxide, anIn—Ga oxide, an In—Ga—Zn oxide, an In—Al—Zn oxide, an In—Sn—Zn oxide, aSn—Ga—Zn oxide, an Al—Ga—Zn oxide, a Sn—Al—Zn oxide, an In—Hf—Zn oxide,an In—La—Zn oxide, an In—Ce—Zn oxide, an In—Pr—Zn oxide, an In—Nd—Znoxide, an In—Sm—Zn oxide, an In—Eu—Zn oxide, an In—Gd—Zn oxide, anIn—Tb—Zn oxide, an In—Dy—Zn oxide, an In—Ho—Zn oxide, an In—Er—Zn oxide,an In—Tm—Zn oxide, an In—Yb—Zn oxide, an In—Lu—Zn oxide, an In—Sn—Ga—Znoxide, an In—Hf—Ga—Zn oxide, an In—Al—Ga—Zn oxide, an In—Sn—Al—Zn oxide,an In—Sn—Hf—Zn oxide, or an In—Hf—Al—Zn oxide.

Note that, for example, an In—Ga—Zn oxide means an oxide containing In,Ga, and Zn as its main components and there is no particular limitationon the ratio of In to Ga and Zn. The In—Ga—Zn oxide may contain anothermetal element in addition to In, Ga, and Zn. In this embodiment, anoxide semiconductor is used for the semiconductor layer 108.

Next, first heat treatment is preferably performed. The first heattreatment may be performed at a temperature higher than or equal to 250°C. and lower than or equal to 650° C., preferably higher than or equalto 300° C. and lower than or equal to 500° C., in an inert gasatmosphere, an atmosphere containing an oxidizing gas at 10 ppm or more,or a reduced pressure state. Alternatively, the first heat treatment maybe performed in such a manner that heat treatment is performed in aninert gas atmosphere, and then another heat treatment is performed in anatmosphere containing an oxidizing gas at 10 ppm or more, in order tocompensate for desorbed oxygen. By the first heat treatment, thecrystallinity of the oxide semiconductor that is used for thesemiconductor layer 108 can be improved, and in addition, impuritiessuch as hydrogen and water can be removed from the insulating layers 106a and 106 b and the semiconductor layer 108. The first heat treatmentmay be performed before processing into the semiconductor layer 108having an island shape.

Next, the opening 132 is formed in a desired region of the insulatinglayers 106 a and 106 b (see FIG. 4D).

Note that the opening 132 is formed so as to reach the conductive layer104 b. The opening 132 can be formed by, for example, wet etching, dryetching, or a combination of wet etching and dry etching.

Next, a conductive layer 109 a, a conductive layer 109 b, and aconductive layer 109 c are formed over the insulating layer 106 b andthe semiconductor layer 108 so as to cover the opening 132 (see FIG.5A).

The conductive layer 109 a serves as a barrier metal. The conductivelayer 109 a can be formed using any material that provides excellentcontact resistance between the conductive layer 109 a and thesemiconductor layer 108. For example, the conductive layer 109 a isformed to have a single-layer structure or a stacked-layer structureincluding any of metals such as titanium, chromium, nickel, yttrium,zirconium, molybdenum, tantalum, and tungsten or an alloy containing anyof these metals as its main component.

The conductive layer 109 b, which is to serve as part of a reflectiveelectrode layer, is preferably formed using a conductive material withhigh reflectivity. Further, the conductive layer 109 b serves as part ofthe source electrode layer and part of the drain electrode layer of thetransistor, and therefore is preferably formed using a low-resistancematerial. For example, the conductive layer 109 b is formed to have asingle-layer structure or a stacked-layer structure including any ofmetals such as aluminum, silver, palladium, and copper or an alloycontaining any of these metals as its main component. It is particularlypreferable to use a material including aluminum for the conductive layer109 b in terms of cost, processability, and the like.

The conductive layer 109 c can be formed using any material thatprovides excellent contact resistance between the conductive layer 109 cand the pixel electrode layer 118 connected later, and a highlyoxidation-resistant conductive layer can be used. Note that theoxidation resistance of the highly oxidation-resistant conductive layeris higher than at least that of a material used for the conductive layer109 b. For example, the conductive layer 109 c is formed to have asingle-layer structure or a stacked-layer structure including any ofmetals such as titanium, chromium, nickel, yttrium, molybdenum,tantalum, and tungsten, an alloy containing any of these metals as itsmain component, or a metal nitride containing any of these materials asits main component. It is particularly preferable to use a materialincluding titanium or molybdenum for the conductive layer 109 c, inwhich case excellent contact resistance between the conductive layer 109c and a material (e.g., indium tin oxide (ITO)) used for the pixelelectrode layer 118 can be provided.

For example, a titanium film or a titanium nitride film is used as theconductive layer 109 a, an aluminum film or a silver film is used as theconductive layer 109 b, and a titanium film or a titanium nitride filmis used as the conductive layer 109 c. Alternatively, a molybdenum filmor a molybdenum nitride film is used as the conductive layer 109 a, analuminum film or a silver film is used as the conductive layer 109 b,and a molybdenum film or a molybdenum nitride film is used as theconductive layer 109 c.

Note that the structures of the conductive layers 109 a, 109 b, and 109c are not limited to the above, and a two-layer structure without theconductive layer 109 a may be employed. An example of the two-layerstructure is a structure in which an aluminum film is used as theconductive layer 109 b and a titanium film is used as the conductivelayer 109 c.

The conductive layers 109 a, 109 b, and 109 c can be formed by asputtering method, for example.

Then, the conductive layer 109 c is processed into a desired shape, sothat the conductive layer 110 c_1 is formed (see FIG. 5B).

The conductive layer 110_1 is formed at least in a region to be incontact with the pixel electrode layer 118 later. A conductive layerdifferent from the conductive layer 110 c_1 may be formed in the samestep as the conductive layer 110 c_1. An example of the conductive layerformed in the same step as the conductive layer 110 c_1 is a conductivelayer formed over a connection portion or an FPC terminal portion.

Note that when the conductive layer 110 c_1 is formed, at least aportion of a surface of the conductive layer 109 b is exposed. A regionof the conductive layer 109 b where the surface is exposed serves as areflective electrode layer later. Examples of a method for forming theconductive layer 110 c_1 include a dry etching method, a wet etchingmethod, and plasma treatment. When the conductive layer 110 c_1 isformed, the surface of the conductive layer 109 b may become uneven. Theuneven surface can diffusely reflect incident light. This is preferablewhen the conductive layer 109 b is used as the reflective electrodelayer because the reflective electrode layer can have improvedreflection efficiency.

Then, the conductive layers 109 a and 109 b are processed into desiredshapes, so that the conductive layers 110 a_1, 110 b_1, 110 a_2, and 110b_2, which serve as the source electrode layer and the drain electrodelayer of the transistor 150, and the conductive layers 110 a_3 and 110b_3, which serve as the reflective electrode layer and one electrode ofthe capacitor 152, are formed. At this stage, the transistor 150 and thecapacitor 152 are formed (see FIG. 5C).

The conductive layers 110 a_1, 110 b_1, 110 a_2, 110 b_2, 110 a_3, and110 b_3 are formed in such a manner that a mask is formed over theconductive layers 109 a and 109 b and regions not covered with the maskare etched. As an etching method for forming the conductive layers 110a_1, 110 b_1, 110 a_2, 110 b_2, 110 a_3, and 110 b_3, a dry etchingmethod or a wet etching method can be used.

When the conductive layers 110 a_1, 110 b_1, 110 a_2, 110 b_2, 110 a_3,and 110 b_3 are formed, the semiconductor layer 108 may be partly etchedto have a depressed portion.

Note that the cross-sectional structure illustrated in FIG. 5C may beformed using a half-tone mask (or a gray-tone mask, a phase-shift mask,or the like). In that case, after the step in FIG. 5A, a cross-sectionalstructure illustrated in FIG. 15 is obtained by etching of theconductive layers 109 a, 109 b and 109 c. After that, the resist is madeslightly smaller by ashing or the like, and then, only part of theconductive layers is etched. As a result, such a cross-sectionalstructure as illustrated in FIG. 5C is obtained. With the use of ahalf-tone mask (or a gray-tone mask, a phase-shift mask, or the like),the number of steps in the process can be reduced. In that case, theconductive layer 110 b_2 or the like is necessarily provided under theconductive layer 110 c_1. Note that one embodiment of the presentinvention is not limited to this example. For example, it is possiblethat the conductive layer 110 b_2 or the like is not provided under theconductive layer 110 c_1 and an insulating film is provided under theconductive layer 110 c_1. Alternatively, for example, after thecross-sectional structure illustrated in FIG. 15 is obtained, theinsulating layer 112 may be formed thereover without etching of theconductive layers.

Next, the insulating layer 112 is formed over the semiconductor layer108, the conductive layers 110 b_1, 110 b_2, 110 b_3, and 110 c_1, andthe insulating layer 106 b (see FIG. 5D).

For the insulating layer 112, an inorganic insulating materialcontaining oxygen can be used in order to improve the characteristics ofthe interface with the oxide semiconductor used for the semiconductorlayer 108. The insulating layer 112 can be formed by a PE-CVD method,for example.

As an example of the insulating layer 112, a silicon oxide film, asilicon oxynitride film, an aluminum oxide film, or the like having athickness of greater than or equal to 50 nm and less than or equal to500 nm can be used. In this embodiment, a 450-nm-thick siliconoxynitride film is used as the insulating layer 112.

Another insulating layer may be formed over the insulating layer 112.The insulating layer is formed using a material that can prevent anexternal impurity such as water, an alkali metal, or an alkaline earthmetal from diffusing into the oxide semiconductor used for thesemiconductor layer 108. For example, a silicon nitride film a siliconnitride oxide film, or the like having a thickness of greater than orequal to 50 nm and less than or equal to 500 nm can be used as theinsulating layer.

The insulating layer 112 over the conductive layer 110 b_3 serving as areflective electrode layer is preferably thin. For example, thethickness of the insulating layer 112 over the conductive layer 110 b_3is preferably greater than or equal to 1 nm and less than or equal to100 nm, further preferably greater than or equal to 5 nm and less thanor equal to 50 nm. Forming the insulating layer 112 thin over theconductive layer 110 b_3 can shorten the optical path length between theconductive layer 110 b_3 and the coloring layer 114. For example, theinsulating layer 112 over the conductive layer 110 b_3 serving as areflective electrode layer is thinned in such a manner that, after theformation of the insulating layer 112, a mask is formed in a regionother than the conductive layer 110 b_3 and the insulating layer 112over the conductive layer 110 b_3 is etched.

Next, the coloring layer 114 having a desired shape is formed over theinsulating layer 112. Then, the insulating layer 116 is formed so as tocover the coloring layer 114 (see FIG. 6A).

The coloring layer 114 is a coloring layer having a function oftransmitting light in a particular wavelength region. For example, a red(R) color filter for transmitting light in a red wavelength range, agreen (G) color filter for transmitting light in a green wavelengthrange, a blue (B) color filter for transmitting light in a bluewavelength range, or the like can be used. Each color filter is formedin a desired position with any of various materials by a printingmethod, an inkjet method, an etching method using a photolithographytechnique, or the like.

Note that the coloring layer 114 has the opening 134 serving as a firstopening and the opening 136 serving as a second opening.

For the insulating layer 116, an organic insulating material such as anacrylic resin can be used. With the insulating layer 116, an impurity orthe like contained in the coloring layer 114 can be prevented fromdiffusing to the liquid crystal layer 166 side, for example. Moreover,the insulating layer 116 can planarize unevenness and the like due tothe transistor 150 or the coloring layer 114.

Note that the insulating layer 116 preferably has an opening insubstantially the same position as the opening 134 in the coloring layer114. The opening is formed so as to expose a portion of a surface of theinsulating layer 112.

Next, the opening 138 is formed (see FIG. 6B).

The opening 138 is formed in a desired region so as to expose theconductive layer 110 c_1. An example of a formation method of theopening 138 is, but is not limited to, a dry etching method.Alternatively, a wet etching method or a combination of dry etching andwet etching can be employed for formation of the opening 138.

Then, the pixel electrode layer 118 is formed in a desired region overthe insulating layer 116 so as to cover the openings 134 and 138 (seeFIG. 6C).

A material having the property of transmitting visible light may be usedfor the pixel electrode layer 118. For example, a material including oneof indium (In), zinc (Zn), and tin (Sn) is preferably used for the pixelelectrode layer 118. The pixel electrode layer 118 can be formed using alight-transmitting conductive material such as indium oxide containingtungsten oxide, indium zinc oxide containing tungsten oxide, indiumoxide containing titanium oxide, indium tin oxide containing titaniumoxide, indium tin oxide (ITO), indium zinc oxide, or indium tin oxide towhich silicon oxide is added. The pixel electrode layer 118 can beformed by a sputtering method, for example.

Note that the pixel electrode layer 118 is connected to the conductivelayer 110 c_1 through the openings 134 and 138. In other words, thepixel electrode layer 118 is electrically connected to the conductivelayers 110 a_2 and 110 b_2 serving as a drain electrode layer of thetransistor 150.

Through the above process, the structure over the first substrate 102can be formed.

Next, the first substrate 102 and the second substrate 162 are attachedto each other and the liquid crystal layer 166 is formed.

Note that the second substrate 162 has the conductive layer 164. Theconductive layer 164, which serves as the other electrode of the liquidcrystal element 170, is preferably formed using a light-transmittingmaterial. For the conductive layer 164, a material that can be used forthe pixel electrode layer 118 can be used.

The liquid crystal layer 166 can be formed by a dispenser method (adropping method), or an injecting method by which a liquid crystal isinjected using a capillary phenomenon after the first substrate 102 andthe second substrate 162 are attached to each other.

There is no particular limitation on materials that can be used for theliquid crystal layer 166, and a nematic liquid crystal material, acholesteric liquid crystal material, or the like may be used, forexample. For the liquid crystal layer 166, a polymer dispersed liquidcrystal, a high molecular compound dispersed liquid crystal, a polymernetwork liquid crystal, or the like may be used.

Through the above process, the display device illustrated in FIG. 1 andFIGS. 3A and 3B can be manufactured.

Although not illustrated, in this embodiment, an alignment film or anoptical film such as a polarizing plate, a circularly polarizing plate(including an elliptically polarizing plate), or a retardation plate (aquarter-wave plate or a half-wave plate) may be provided as appropriateif necessary. Furthermore, the polarizing plate or the circularlypolarizing plate may be provided with an anti-reflection film. Forexample, anti-glare treatment by which reflected light can be diffusedby projections and depressions on the surface so as to reduce the glarecan be performed.

Although the case of a reflective display device is described in thisembodiment, one embodiment of the present invention is not limited tothis example. For example, in an aperture portion of a pixel, atransmissive region may be provided. For example, in one part of anaperture portion of a pixel, a reflective region may be provided, and inanother part thereof, a transmissive region may be provided. Therefore,one embodiment of the present invention can also be applied to asemi-transmissive display device.

Although the example in which the coloring layer 114 is provided withthe openings 136 is described in this embodiment, one embodiment of thepresent invention is not limited to this example. Depending oncircumstances or conditions, the coloring layer 114 is not necessarilyprovided with the openings 136. For example, it is possible that theopening 136 is not provided in at least one of R, G, and B pixels.Alternatively, in the case where a transmissive region and a reflectiveregion are provided in an aperture portion of a pixel, it is possiblethat the coloring layer 114 is provided with the opening 136 in thereflective region and the coloring layer 114 is not provided with theopening 136 in the transmissive region.

Although the example in which the coloring layer 114 is provided overthe first substrate 102 is described in this embodiment, one embodimentof the present invention is not limited to this example. Depending oncircumstances or conditions, the coloring layer 114 is not necessarilyprovided over the first substrate 102. For example, in the case where aW (white) pixel is used in addition to the R, G, and B pixels, it ispossible that the coloring layer 114 is not provided over the firstsubstrate 102.

This embodiment can be combined with any of the other embodiments inthis specification as appropriate.

Embodiment 2

In this embodiment, a modification example of the display devicedescribed in Embodiment 1 is described with reference to FIGS. 7A and7B. Note that portions having functions similar to those in Embodiment 1are given the same reference numerals and detailed description thereofis omitted.

FIG. 7A is a cross-sectional view corresponding to a cross section takenalong dashed-dotted line X1-Y1 in FIG. 1. FIG. 7B is a cross-sectionalview illustrating an example of a method for manufacturing the displaydevice illustrated in FIG. 7A.

The display device in FIG. 7A includes a first substrate 202; anadhesive layer 203 over the first substrate 202; an insulating layer 205over the adhesive layer 203; the conductive layer 104 a serving as agate electrode layer over the insulating layer 205; the conductive layer104 b formed in the same step as the conductive layer 104 a; theinsulating layers 106 a and 106 b over the insulating layer 205 and theconductive layers 104 a and 104 b; the semiconductor layer 108 which isover the insulating layer 106 b and overlaps with the conductive layer104 a; the conductive layer 110 a_1 serving as a source electrode layerover the semiconductor layer 108 and the insulating layer 106 b; theconductive layer 110 a_2 serving as a drain electrode layer over thesemiconductor layer 108 and the insulating layer 106 b; the conductivelayer 110 a_3 formed in the same step as the conductive layers 110 a_1and 110 a_2; the conductive layers 110 b_1, 110 b_2, and 110 b_3 overthe conductive layers 110 a_1, 110 a_2, and 110 a_3; the conductivelayer 110 c_1 over the conductive layer 110 b_2; the insulating layer112 serving as a protective insulating film over the insulating layer106 b, the semiconductor layer 108, and the conductive layers 110 b_1,110 b_2, 110 b_3, and 110 c_1; the coloring layer 114 having a functionof a color filter over the insulating layer 112; the insulating layer116 having a function of an overcoat layer over the coloring layer 114;the pixel electrode layer 118 over the insulating layer 116; the liquidcrystal layer 166 over the pixel electrode layer 118; the conductivelayer 164 having a function of a counter electrode over the liquidcrystal layer 166; an insulating layer 209 over the conductive layer164; an adhesive layer 207 over the insulating layer 209; and a secondsubstrate 262 over the adhesive layer 207.

Note that the conductive layer 104 a, the insulating layers 106 a and106 b, the semiconductor layer 108, and the conductive layers 110 a_1,110 a_2, 110 b_1, and 110 b_2 form the transistor 150. The conductivelayer 104 b, the insulating layers 106 a and 106 b, and the conductivelayers 110 a_3 and 110 b_3 form the capacitor 152.

Note that portions of the insulating layers 106 a and 106 b overlappingwith the conductive layer 104 a serving as a gate electrode layer have afunction of the gate insulating layer of the transistor 150. Inaddition, portions of the insulating layers 106 a and 106 b overlappingwith the conductive layer 104 b have a function of a dielectric layer ofthe capacitor 152.

The insulating layers 106 a and 106 b are provided with the opening 132which reaches the conductive layer 104 b, and the conductive layers 110a_2 and 110 b_2 having a function of a drain electrode layer of thetransistor 150 are connected to the conductive layer 104 b through theopening 132.

The coloring layer 114 is provided with the opening 134 and the openings136. In other words, the insulating layer 116 over the coloring layer114 is in contact with the insulating layer 112 in the opening 134. Notethat the adhesion of the insulating layer 116 to the insulating layer112 is higher than that of the coloring layer 114. Therefore, when thereis a region where the insulating layer 116 and the insulating layer 112are in contact with each other, separation of the coloring layer 114 canbe suppressed even in the case where the adhesion between the coloringlayer 114 and the insulating layer 112 is not sufficient.

The color purity of the coloring layer 114 can be adjusted with theopenings 136 provided in the coloring layer 114. For example, the colorpurity of the coloring layer 114 can be adjusted by adjusting the shapeof the openings 136 or the area of the openings 136.

With such a structure in which the coloring layer 114 has the openings136, a novel display device capable of adjusting color purity can beprovided. It addition, a novel display device with improved adhesion ofthe coloring layer 114 used as a color filter can be provided.

Note that the display device in FIG. 7A differs from the display devicein FIG. 3A in the following points. In the display device in FIG. 7A,the first substrate 202 is provided instead of the first substrate 102,and the second substrate 262 is provided instead of the second substrate162. In addition, in the display device in FIG. 7A, the adhesive layer203 and the insulating layer 205 are provided between the firstsubstrate 202 and the conductive layers 104 a and 104 b. Furthermore, inthe display device in FIG. 7A, the adhesive layer 207 and the insulatinglayer 209 are provided between the second substrate 262 and theconductive layer 164.

For the first substrate 202 and the second substrate 262, a materialhaving flexibility can be used. It is preferable to use a materialhaving flexibility and toughness for the first substrate 202 and thesecond substrate 262. Examples of the material having flexibilityinclude an organic resin and glass thin enough to have flexibility.

An organic resin, which has a specific gravity smaller than that ofglass, is preferably used for the first substrate 202 and the secondsubstrate 262, in which case the display device can be more lightweightas compared with the case where glass is used.

Examples of the material having flexibility include glass thin enough tohave flexibility, polyester resins such as polyethylene terephthalate(PET) and polyethylene naphthalate (PEN), a polyacrylonitrile resin, apolyimide resin, a polymethyl methacrylate resin, a polycarbonate (PC)resin, a polyethersulfone (PES) resin, a polyamide resin, a cycloolefinresin, a polystyrene resin, a polyamide imide resin, a polyvinylchloride resin, and a polyether ether ketone (PEEK) resin. Inparticular, a material whose coefficient of thermal expansion is low ispreferable, and for example, a polyamide imide resin, a polyimide resin,or PET can be suitably used. A substrate in which a glass fiber isimpregnated with an organic resin or a substrate whose coefficient ofthermal expansion is reduced by mixing an organic resin with aninorganic filler can also be used.

In the case where a fibrous body is contained in the material havingflexibility, a high-strength fiber of an organic compound or aninorganic compound is used as the fibrous body. A high-strength fiber isspecifically a fiber with a high tensile modulus of elasticity or afiber with a high Young's modulus. Typical examples of a high-strengthfiber include a polyvinyl alcohol based fiber, a polyester based fiber,a polyamide based fiber, a polyethylene based fiber, an aramid basedfiber, a polyparaphenylene benzobisoxazole fiber, a glass fiber, and acarbon fiber. As the glass fiber, glass fiber using E glass, S glass, Dglass, Q glass, or the like can be used. These fibers may be used in astate of a woven fabric or a nonwoven fabric, and a structure in whichthis fibrous body is impregnated with a resin and the resin is cured maybe used. The structure including the fibrous body and the resin ispreferably used, in which case the reliability against bending orbreaking due to local pressure can be increased.

To improve the light extraction efficiency, the refractive index of thematerial having flexibility is preferably high. For example, a substrateobtained by dispersing an inorganic filler having a high refractiveindex into an organic resin can have a higher refractive index than thesubstrate formed of only the organic resin. In particular, an inorganicfiller having a particle diameter as small as 40 nm or less ispreferable, in which case such a filler can maintain opticaltransparency.

The first substrate 202 and the second substrate 262 may have astacked-layer structure in which a hard coat layer (such as a siliconnitride layer) by which a surface of a display device is protected fromdamage, a layer (such as an aramid resin layer) which can dispersepressure, or the like is stacked over a surface of any of theabove-mentioned materials having flexibility.

As the adhesive layers 203 and 207, various curable adhesives such as areactive curable adhesive, a thermosetting adhesive, an anaerobicadhesive, and a photo-curable adhesive such as an ultraviolet curableadhesive can be used. Examples of such adhesives include an epoxy resin,an acrylic resin, a silicone resin, a phenol resin, a polyimide resin,an imide resin, a polyvinyl chloride (PVC) resin, a polyvinyl butyral(PVB) resin, and an ethylene vinyl acetate (EVA) resin. In particular, amaterial with low moisture permeability, such as an epoxy resin, ispreferred. Alternatively, a two-component-mixture-type resin may beused. Further alternatively, an adhesive sheet or the like may be used.

The adhesive layers 203 and 207 may include a drying agent in a resinmaterial. As the drying agent, for example, a substance which adsorbsmoisture by chemical adsorption, such as an oxide of an alkaline earthmetal (e.g., calcium oxide or barium oxide), can be used. Alternatively,a substance that adsorbs moisture by physical adsorption, such aszeolite or silica gel, may be used. The drying agent is preferablyincluded, in which case it can suppress entry of impurities such asmoisture into the display device.

For the insulating layers 205 and 209, an inorganic insulating materialcan be used, for example. The inorganic insulating material may have asingle-layer structure or a multilayer structure of silicon nitride,silicon oxynitride, silicon nitride oxide, aluminum oxide, or the like.The insulating layers 205 and 209 have a function of buffer layers.

There is no particular limitation on the method for forming theinsulating layers 205 and 209; a sputtering method, an evaporationmethod, a droplet discharging method (e.g., an ink-jet method), aprinting method (e.g., a screen printing method or an off-set printingmethod), or the like may be used.

Here, an example of a method for manufacturing the display deviceillustrated in FIG. 7A is described with reference to FIG. 7B.

As illustrated in FIG. 7B, a separation layer 211 is formed over thefirst substrate 102. Next, the insulating layer 205 is formed over theseparation layer 211.

For the first substrate 102, any of the materials described inEmbodiment 1 can be used.

The separation layer 211 can be formed to have a single-layer structureor a stacked-layer structure using an element selected from tungsten,molybdenum, titanium, tantalum, niobium, nickel, cobalt, zirconium,zinc, ruthenium, rhodium, palladium, osmium, iridium, and silicon; analloy material containing any of the elements; a compound materialcontaining any of the elements; or the like, for example. In the case ofa layer containing silicon, a crystal structure of the layer containingsilicon may be amorphous, microcrystal, polycrystal, or single crystal.

Note that between the first substrate 102 and the separation layer 211,an insulating film such as a silicon oxide film, a silicon oxynitridefilm, a silicon nitride film, or a silicon nitride oxide film may beformed. The insulating film is preferably formed because it can suppressentry of impurities which can be contained in the first substrate 102 tothe separation layer 211 side.

The separation layer 211 can be formed by a sputtering method, a plasmaCVD method, a coating method, a printing method, or the like. Note thata coating method includes a spin coating method, a droplet dischargemethod, and a dispensing method.

In the case where the separation layer 211 has a single-layer structure,a layer containing tungsten, molybdenum, or a mixture of tungsten andmolybdenum is preferably formed. Alternatively, a layer containing anoxide or an oxynitride of tungsten, a layer containing an oxide or anoxynitride of molybdenum, or a layer containing an oxide or anoxynitride of a mixture of tungsten and molybdenum may be formed. Notethat the mixture of tungsten and molybdenum corresponds to an alloy oftungsten and molybdenum, for example.

In the case where the separation layer 211 is formed to have astacked-layer structure including a layer containing tungsten and alayer containing an oxide of tungsten, the layer containing an oxide oftungsten may be formed as follows: the layer containing tungsten isformed first and an insulating layer formed of an oxide is formedthereover, so that the layer containing an oxide of tungsten is formedat the interface between the tungsten layer and the insulating layer.Alternatively, the layer containing an oxide of tungsten may be formedby performing thermal oxidation treatment, oxygen plasma treatment,nitrous oxide (N₂O) plasma treatment, treatment with a highly oxidizingsolution such as ozone water, or the like on the surface of the layercontaining tungsten. Plasma treatment or heat treatment may be performedin an atmosphere of oxygen, nitrogen, or nitrous oxide alone, or a mixedgas of any of these gasses and another gas. Surface condition of theseparation layer 211 is changed by the plasma treatment or heattreatment, whereby adhesion between the separation layer 211 and theinsulating layer 205 formed later can be controlled.

In this embodiment, a 30-nm-thick tungsten film is formed as theseparation layer 211 by a sputtering method.

The insulating layer 205 can be formed using any of the above-listedmaterials. For example, in this embodiment, the insulating layer 205 isformed at a temperature of higher than or equal to 250° C. and lowerthan or equal to 400° C. by a plasma CVD method, whereby the insulatinglayer 205 can be a dense film with low water permeability. Note that thethickness of the insulating layer 205 is preferably greater than orequal to 10 nm and less than or equal to 3000 nm, further preferablygreater than or equal to 200 nm and less than or equal to 1500 nm. Inthis embodiment, a 600-nm-thick silicon oxynitride film is formed by aplasma CVD method and then a 200-nm-thick silicon nitride film is formedover the silicon oxynitride by a plasma CVD method.

Next, the conductive layers 104 a and 104 b are formed over theinsulating layer 205. Subsequent steps are similar to those forcomponents in Embodiment 1; thus, components can be formed withreference to the description in Embodiment 1.

Next, a material to be an adhesive layer is applied to an elementsubstrate where the transistor 150, the capacitor 152, and the like areformed (in FIG. 7B, to the insulating layer 116 and the pixel electrodelayer 118), and the element substrate is attached to a support substratewith the adhesive layer. Then, separation is caused between theseparation layer 211 and the insulating layer 205 over the firstsubstrate 102, and the insulating layer 205 in an exposed state and thefirst substrate 202 are attached to each other with the adhesive layer203.

Note that any of a variety of methods can be used as appropriate in thestep of causing separation between the separation layer 211 and theinsulating layer 205. For example, when a layer including a metal oxidefilm is formed as the separation layer 211 on the side in contact with alayer to be separated (in FIG. 7B, the insulating layer 205, which mayalso be referred to as a layer to be separated below), the metal oxidefilm is embrittled by crystallization, whereby the layer to be separatedcan be separated from the first substrate 102.

Alternatively, when a substrate having high heat resistance is used asthe first substrate 102 and when an amorphous silicon film containinghydrogen is formed as the separation layer 211 between the substratehaving high heat resistance and the layer to be separated, the amorphoussilicon film is removed by laser light irradiation or etching, wherebythe layer to be separated can be separated from the first substrate 102.

Alternatively, after a layer including a metal oxide film is formed asthe separation layer 211 on the side in contact with the layer to beseparated, the metal oxide film is embrittled by crystallization, andpart of the separation layer is removed by etching using a solution or afluoride gas such as NF₃. BrF₃, or ClF₃, whereby the separation can beperformed at the embrittled metal oxide film.

A method may be used in which a film containing nitrogen, oxygen,hydrogen, or the like (for example, an amorphous silicon film containinghydrogen, an alloy film containing hydrogen, an alloy film containingoxygen, or the like) is used as the separation layer 211, and theseparation layer 211 is irradiated with laser light to release nitrogen,oxygen, or hydrogen contained in the separation layer 211 as a gas,thereby promoting separation between the layer to be separated and thesubstrate.

Further, the separation process can be conducted easily by combinationof the above-described separation steps. For example, separation can beperformed with physical force (by a machine or the like) afterperforming laser light irradiation, etching on the separation layer witha gas, a solution, or the like, or mechanical removal with a sharpknife, a scalpel, or the like so that the separation layer and the layerto be separated can be easily separated from each other.

Separation of the layer to be separated from the first substrate 102 maybe carried out by filling the interface between the separation layer 211and the layer to be separated with a liquid. Further, the separation maybe conducted while pouring a liquid such as water. In the case where theseparation layer 211 is formed using a tungsten film, it is preferablethat the separation be performed while etching the tungsten film using amixed solution of ammonia water and a hydrogen peroxide solution.

Note that the separation layer 211 is not necessary in the case whereseparation at the interface between the first substrate 102 and thelayer to be separated is possible. For example, glass is used as thefirst substrate 102, an organic resin such as polyimide is formed incontact with the glass, and an insulating film, a transistor, and thelike are formed over the organic resin. In this case, heating theorganic resin enables the separation at the interface between the firstsubstrate 102 and the organic resin. Alternatively, separation at theinterface between a metal layer and the organic resin may be performedin the following manner: the metal layer is provided between the firstsubstrate 102 and the organic resin and current is made to flow in themetal layer so that the metal layer is heated.

Through the above steps, the transistor 150, the capacitor 152, and thelike formed over the first substrate 102 can be transferred to the firstsubstrate 202 having flexibility.

Note that transfer from the second substrate 162 to the second substrate262 can be performed by a similar method. Note that the second substrate262 is not provided with elements such as the transistor 150 and thecapacitor 152, therefore, the conductive layer 164 may be formeddirectly over the second substrate 262. In that case, the adhesive layer207 and the insulating layer 209 are not provided.

Next, the first substrate 202 and the second substrate 262 are attachedand the liquid crystal layer 166 is injected between the first substrate202 and the second substrate 262. Thus, the display device in FIG. 7Acan be formed.

Since the first substrate 202 and the second substrate 262 of thematerial having flexibility are used in the display device described inthis embodiment, the display device can be flexible. In the case wherethe material having flexibility and toughness is used for each of thefirst and second substrates 202 and 262, a display device with highimpact resistance that is less likely to be broken can be obtained.

In the display device in FIG. 7A, the insulating layer 116 and theinsulating layer 112 are in contact with each other in the opening 134and the opening 136. Accordingly, the adhesion of the coloring layer 114is increased, and separation of the coloring layer 114 can be suppressedeven in a flexible structure. This is an advantageous effect obtained inone embodiment of the present invention. As described above, the displaydevice of one embodiment of the present invention, in which the adhesionof the coloring layer 114 is increased, is particularly effective in aflexible structure.

Note that a substrate formed using the material having flexibility maybe similarly used in other drawings such as FIGS. 16A and 16B, FIGS. 17Aand 17B, FIGS. 18A and 18B, FIGS. 19A and 19B, and FIGS. 20A and 20B.

This embodiment can be combined with any of the other embodiments asappropriate.

Embodiment 3

In this embodiment, a display device of one embodiment of the presentinvention will be described with reference to FIGS. 8A and 8B. Note thatportions having functions similar to those in Embodiments 1 and 2 aregiven the same reference numerals and detailed description thereof isomitted.

The display device illustrated in FIG. 8A includes a pixel portionincluding pixel regions with display elements (hereinafter, the portionis referred to as a pixel portion 302), a circuit portion being providedoutside the pixel portion 302 and including a circuit for driving thepixel portion 302 (hereinafter, the portion is referred to as a drivercircuit portion 304), circuits each having a function of protecting anelement (hereinafter, the circuits are referred to as protection circuitportions 306), and a terminal portion 307. Note that the protectioncircuit portions 306 are not necessarily provided.

A part or the whole of the driver circuit portion 304 is preferablyformed over a substrate over which the pixel portion 302 is formed, inwhich case the number of components and the number of terminals can bereduced. When a part or the whole of the driver circuit portion 304 isnot formed over the substrate over which the pixel portion 302 isformed, the part or the whole of the driver circuit portion 304 can bemounted by chip-on-glass (COG) or tape automated bonding (TAB).

The pixel portion 302 includes a plurality of circuits for drivingdisplay elements arranged in X rows (X is a natural number of 2 or more)and Y columns (Y is a natural number of 2 or more) (hereinafter, suchcircuits are referred to as pixel circuits 308). The driver circuitportion 304 includes driver circuits such as a circuit for supplying asignal (scan signal) to select a pixel (hereinafter, the circuit isreferred to as a gate driver 304 a) and a circuit for supplying a signal(data signal) to drive a display element in a pixel (hereinafter, thecircuit is referred to as a source driver 304 b).

The gate driver 304 a includes a shift register or the like. The gatedriver 304 a receives a signal for driving the shift register throughthe terminal portion 307 and outputs a signal. For example, the gatedriver 304 a receives a start pulse signal, a clock signal, or the likeand outputs a pulse signal. The gate driver 304 a has a function ofcontrolling the potentials of wirings supplied with scan signals(hereinafter, such wirings are referred to as gate lines GL_1 to GL_X,and the gate lines may also be referred to as scan lines). Note that aplurality of gate drivers 304 a may be provided to control the gatelines GL_1 to GL_X separately. Alternatively, the gate driver 304 a hasa function of supplying an initialization signal. Without being limitedthereto, the gate driver 304 a can supply another signal.

The source driver 304 b includes a shift register or the like. Thesource driver 304 b receives a signal (video signal) from which a datasignal is derived, as well as a signal for driving the shift register,through the terminal portion 307. The source driver 304 b has a functionof generating a data signal to be written to the pixel circuit 308 whichis based on the video signal. In addition, the source driver 304 b has afunction of controlling output of a data signal in response to a pulsesignal produced by input of a start pulse signal, a clock signal, or thelike. Further, the source driver 304 b has a function of controlling thepotentials of wirings supplied with data signals (hereinafter, suchwirings are referred to as source lines DL_1 to DL_Y, and the sourcelines may also be referred to as data lines). Alternatively, the sourcedriver 304 b has a function of supplying an initialization signal.Without being limited thereto, the source driver 304 b can supplyanother signal.

The source driver 304 b includes a plurality of analog switches or thelike, for example. The source driver 304 b can output, as the datasignals, signals obtained by time-dividing the video signal bysequentially turning on the plurality of analog switches. The sourcedriver 304 b may include a shift register or the like.

A pulse signal and a data signal are input to each of the plurality ofpixel circuits 308 through one of the plurality of gate lines GLsupplied with scan signals and one of the plurality of source lines DLsupplied with data signals, respectively. Writing and holding of thedata signal to and in each of the plurality of pixel circuits 308 arecontrolled by the gate driver 304 a. For example, to the pixel circuit308 in the m-th row and the n-th column (m is a natural number of lessthan or equal to X, and n is a natural number of less than or equal toY), a pulse signal is input from the gate driver 304 a through the gateline GL_m, and a data signal is input from the source driver 304 bthrough the source line DL_n in accordance with the potential of thegate line GL_m.

The protection circuit portion 306 shown in FIG. 8A is connected to, forexample, the gate line GL between the gate driver 304 a and the pixelcircuit 308. Alternatively, the protection circuit portion 306 isconnected to the source line DL between the source driver 304 b and thepixel circuit 308. Alternatively, the protection circuit portion 306 canbe connected to a wiring between the gate driver 304 a and the terminalportion 307. Alternatively, the protection circuit portion 306 can beconnected to a wiring between the source driver 304 b and the terminalportion 307. Note that the terminal portion 307 means a portion havingterminals for inputting power, control signals, and video signals to thedisplay device from external circuits.

The protection circuit portion 306 is a circuit that electricallyconnects a wiring connected to the protection circuit portion to anotherwiring when a potential out of a certain range is applied to the wiringconnected to the protection circuit portion.

As illustrated in FIG. 8A, the protection circuit portions 306 areprovided for the pixel portion 302 and the driver circuit portion 304,so that the resistance of the display device to overcurrent generated byelectrostatic discharge (ESD) or the like can be improved. Note that theconfiguration of the protection circuit portions 306 is not limited tothat, and for example, a configuration in which the protection circuitportions 306 are connected to the gate driver 304 a or a configurationin which the protection circuit portions 306 are connected to the sourcedriver 304 b may be employed. Alternatively, the protection circuitportions 306 may be configured to be connected to the terminal portion307.

In FIG. 8A, an example in which the driver circuit portion 304 includesthe gate driver 304 a and the source driver 304 b is shown; however, thestructure is not limited thereto. For example, only the gate driver 304a may be formed and a separately prepared substrate where a sourcedriver circuit is formed (e.g., a driver circuit substrate formed with asingle crystal semiconductor film or a polycrystalline semiconductorfilm) may be mounted.

Each of the plurality of pixel circuits 308 in FIG. 8A can have astructure illustrated in FIG. 8B, for example.

The pixel circuit 308 illustrated in FIG. 8B includes the liquid crystalelement 170, the transistor 150, and the capacitor 152. Note that theliquid crystal element 170, the transistor 150, and the capacitor 152can be those in the display device in FIGS. 3A and 3B described inEmbodiment 1.

The potential of one of a pair of electrodes of the liquid crystalelement 170 is set in accordance with the specifications of the pixelcircuit 308 as appropriate. The alignment state of the liquid crystalelement 170 depends on written data. A common potential may be suppliedto one of the pair of electrodes of the liquid crystal element 170included in each of the plurality of pixel circuits 308. Further, thepotential supplied to one of the pair of electrodes of the liquidcrystal element 170 in the pixel circuit 308 in one row may be differentfrom the potential supplied to one of the pair of electrodes of theliquid crystal element 170 in the pixel circuit 308 in another row.

As examples of a driving method of the display device including theliquid crystal element 170, any of the following modes can be given: aTN mode, an STN mode, a VA mode, an axially symmetric aligned micro-cell(ASM) mode, an optically compensated birefringence (OCB) mode, aferroelectric liquid crystal (FLC) mode, an antiferroelectric liquidcrystal (AFLC) mode, an MVA mode, a patterned vertical alignment (PVA)mode, an IPS mode, an FFS mode, a transverse bend alignment (TBA) mode,and the like. Other examples of the driving method of the display deviceinclude an electrically controlled birefringence (ECB) mode, a polymerdispersed liquid crystal (PDLC) mode, a polymer network liquid crystal(PNLC) mode, and a guest-host mode. Note that the present invention isnot limited to these examples, and various liquid crystal elements anddriving methods can be applied to the liquid crystal element and thedriving method thereof.

The liquid crystal element may be formed using a liquid crystalcomposition including liquid crystal exhibiting a blue phase and achiral material. The liquid crystal exhibiting a blue phase has a shortresponse time of 1 msec or less and is optically isotropic. Therefore,alignment treatment is not necessary and viewing angle dependence issmall.

In the pixel circuit 308 in the m-th row and the n-th column, one of asource and a drain of the transistor 150 is electrically connected tothe source line DL_n, and the other is electrically connected to theother of the pair of electrodes of the liquid crystal element 170. Agate of the transistor 150 is electrically connected to the gate lineGL_m. The transistor 150 has a function of controlling whether to writea data signal by being turned on or off.

One of a pair of electrodes of the capacitor 152 is electricallyconnected to a wiring to which a potential is supplied (hereinafterreferred to as a potential supply line VL), and the other iselectrically connected to the other of the pair of electrodes of theliquid crystal element 170. The potential of the potential supply lineVL is set in accordance with the specifications of the pixel circuit 308as appropriate. The capacitor 152 functions as a storage capacitor forstoring written data.

For example, in the display device including the pixel circuit 308 inFIG. 8A, the pixel circuits 308 are sequentially selected row by row bythe gate driver 304 a, whereby the transistors 150 are turned on and adata signal is written.

When the transistors 150 are turned off, the pixel circuits 308 in whichthe data has been written are brought into a holding state. Thisoperation is sequentially performed row by row; thus, an image can bedisplayed.

The structure described in this embodiment can be combined with any ofthe structures described in the other embodiments as appropriate.

Embodiment 4

In this embodiment, a display module and electronic devices that can beformed using a display device of one embodiment of the present inventionare described with reference to FIG. 9 and FIGS. 10A to 10H.

In a display module 8000 illustrated in FIG. 9, a touch panel 8004connected to an FPC 8003, a display panel 8006 connected to an FPC 8005,a backlight unit 8007, a frame 8009, a printed board 8010, and a battery8011 are provided between an upper cover 8001 and a lower cover 8002.

The display device of one embodiment of the present invention can beused for, for example, the display panel 8006.

The shapes and sizes of the upper cover 8001 and the lower cover 8002can be changed as appropriate in accordance with the sizes of the touchpanel 8004 and the display panel 8006.

The touch panel 8004 can be a resistive touch panel or a capacitivetouch panel and can be formed to overlap with the display panel 8006. Acounter substrate (sealing substrate) of the display panel 8006 can havea touch panel function. A photosensor may be provided in each pixel ofthe display panel 8006 to form an optical touch panel.

The backlight unit 8007 includes a light source 8008. Note that althougha structure in which the light sources 8008 are provided over thebacklight unit 8007 is illustrated in FIG. 9, one embodiment of thepresent invention is not limited to this structure. For example, astructure in which the light source 8008 is provided at an end portionof the backlight unit 8007 and a light diffusion plate is furtherprovided may be employed.

Note that the backlight unit 8007 need not be provided in the case of areflective liquid crystal display device. The backlight unit 8007 isprovided in the case of a transmissive liquid crystal display device ora semi-transmissive liquid crystal display device, for example.

The frame 8009 protects the display panel 8006 and also functions as anelectromagnetic shield for blocking electromagnetic waves generated bythe operation of the printed board 8010. The frame 8009 may function asa radiator plate.

The printed board 8010 is provided with a power supply circuit and asignal processing circuit for outputting a video signal and a clocksignal. As a power source for supplying power to the power supplycircuit, an external commercial power source or a power source using thebattery 8011 provided separately may be used. The battery 8011 can beomitted in the case of using a commercial power source.

The display module 8000 may be additionally provided with a member suchas a polarizing plate, a retardation plate, or a prism sheet.

FIGS. 10A to 10H illustrate electronic devices. These electronic devicescan include a housing 5000, a display portion 5001, a speaker 5003, anLED lamp 5004, operation keys 5005 (including a power switch or anoperation switch), a connection terminal 5006, a sensor 5007 (a sensorhaving a function of measuring or sensing force, displacement, position,speed, acceleration, angular velocity, rotational frequency, distance,light, liquid, magnetism, temperature, chemical substance, sound, time,hardness, electric field, current, voltage, electric power, radiation,flow rate, humidity, gradient, oscillation, odor, or infrared ray), amicrophone 5008, and the like.

FIG. 10A illustrates a mobile computer that can include a switch 5009,an infrared port 5010, and the like in addition to the above components.FIG. 10B illustrates a portable image reproducing device (e.g., a DVDplayer) that is provided with a memory medium and can include a seconddisplay portion 5002, a memory medium reading portion 5011, and the likein addition to the above components. FIG. 10C illustrates a goggle-typedisplay that can include the second display portion 5002, a support5012, an earphone 5013, and the like in addition to the abovecomponents. FIG. 10D illustrates a portable game machine that caninclude the memory medium reading portion 5011 and the like in additionto the above components. FIG. 10E illustrates a digital camera that hasa television reception function and can include an antenna 5014, ashutter button 5015, an image receiving portion 5016, and the like inaddition to the above components. FIG. 10F illustrates a portable gamemachine that can include the second display portion 5002, the memorymedium reading portion 5011, and the like in addition to the abovecomponents. FIG. 10G illustrates a television receiver that can includea tuner, an image processing portion, and the like in addition to theabove components. FIG. 10H illustrates a portable television receiverthat can include a charger 5017 capable of transmitting and receivingsignals, and the like in addition to the above components.

The electronic devices illustrated in FIGS. 10A to 10H can have avariety of functions, for example, a function of displaying a variety ofdata (a still image, a moving image, a text image, and the like) on thedisplay portion, a touch panel function, a function of displaying acalendar, date, time, and the like, a function of controlling a processwith a variety of software (programs), a wireless communicationfunction, a function of being connected to a variety of computernetworks with a wireless communication function, a function oftransmitting and receiving a variety of data with a wirelesscommunication function, a function of reading a program or data storedin a memory medium and displaying the program or data on the displayportion, and the like. Further, the electronic device including aplurality of display portions can have a function of displaying imagedata mainly on one display portion while displaying text data on anotherdisplay portion, a function of displaying a three-dimensional image bydisplaying images on a plurality of display portions with a parallaxtaken into account, or the like. Furthermore, the electronic deviceincluding an image receiving portion can have a function of shooting astill image, a function of taking a moving image, a function ofautomatically or manually correcting a shot image, a function of storinga shot image in a memory medium (an external memory medium or a memorymedium incorporated in the camera), a function of displaying a shotimage on the display portion, or the like. Note that functions that canbe provided for the electronic devices illustrated in FIGS. 10A to 10Hare not limited to those described above, and the electronic devices canhave a variety of functions.

The electronic devices described in this embodiment each include thedisplay portion for displaying some sort of data.

The structure described in this embodiment can be combined with any ofthe structures described in the other embodiments as appropriate.

Embodiment 5

In this embodiment, a modification example of the display devicedescribed in Embodiment 1 is described with reference to FIG. 21, FIGS.22A and 22B, and FIGS. 23A and 23B. Note that portions having functionssimilar to those in Embodiment 1 are given the same reference numeralsand detailed description thereof is omitted.

FIG. 21 is a top view of an example of a display device of oneembodiment of the present invention. In the top view of FIG. 21, whichshows some pixel regions (three pixels) in the display device,components such as a gate insulating layer are partly omitted to avoidcomplexity. FIG. 23A is a cross-sectional view corresponding to a crosssection taken along dashed-dotted line X6-Y6 in FIG. 21. FIG. 23B is across-sectional view corresponding to a cross section taken alongdashed-dotted line X7-Y7 in FIG. 21.

This embodiment describes an example in which a pixel electrode layer isused as a reflective electrode and a substrate 162 that is a countersubstrate is provided with a coloring layer, a BM 180, and a spacer 181.The position of overlap with openings in the coloring layer and theposition of overlap with the spacer 181 are indicated by dotted lines.The transistor 150 has the same structure as that in Embodiment 1 exceptthat a 400-nm-thick tungsten film is used as a conductive layer; thus,detailed description is omitted here. Note that the transistor 150 has achannel length L of 3 μm and a channel width W of 3 μm. The transistor150 includes a 50-nm-thick In—Ga—Zn oxide (In:Ga:Zn=1:1:1 (at. %))semiconductor layer formed with a sputtering apparatus.

The pixel electrode layer 118 electrically connected to the transistor150 through the opening 138 overlaps with part of the gate line 104, andhas a large reflection area. Note that the transistor 150 is positionedso as to overlap with the BM 180. As the BM 180, a 200-nm-thick titaniumfilm formed with a sputtering apparatus is used.

This embodiment describes an example in which openings in the coloringlayers 114 have different shapes for different colors of pixels, asillustrated in FIGS. 22A and 22B.

FIG. 22A illustrates a structure of a B pixel on the counter substrateside. In FIG. 22A, the proportion of the area of the coloring layer 114to the area of the pixel region 120 is 74.6%. Note that the area of thecoloring layer 114 is calculated by subtracting the area of the BM 180from the area of the pixel region 120. FIG. 22B illustrates a structureof each of R and G pixels on the counter substrate side. In FIG. 22B,the proportion of the area of the coloring layer 114 to the area of thepixel region 120 is 44.4%. When the upper surface shape of the coloringlayer 114 in each of the R and G pixels is different from the uppersurface shape of the coloring layer 114 in the B pixel, and when thearea of the coloring layer 114 in the B pixel is larger than that of thecoloring layer 114 in the R or G pixel, reflectance can be improved withan NTSC ratio maintained.

In each of FIGS. 22A and 22B, a region overlapping with the opening 138is indicated by a dashed-dotted line for easy understanding ofpositional relationship; this does not mean that the structure on thecounter substrate side actually has the opening 138. In addition, inFIG. 21, the opening 136 and the spacer 181 are indicated by dottedlines for easy understanding of positional relationship; only thepositions are indicated and this does not mean that the structure on theside of the substrate provided with the transistor has the opening 136and the spacer 181.

The upper surface shapes of the openings illustrated in FIGS. 22A and22B are examples, to which the present invention is not limited, and maybe triangular, circular, elliptical, polygonal, or the like or acombination of a plurality of kinds of these shapes. In addition, thetotal area of the openings in the coloring layer 114 in the B pixel isat least smaller than that of the openings in the coloring layer 114 ineach of the R and G pixels.

The display device in FIG. 23A includes the first substrate 102; theconductive layer 104 a serving as a gate electrode layer over the firstsubstrate 102; the conductive layer 104 b formed in the same step as theconductive layer 104 a; the insulating layers 106 a and 106 b over thefirst substrate 102 and the conductive layers 104 a and 104 b; thesemiconductor layer 108 which is over the insulating layer 106 b andoverlaps with the conductive layer 104 a; the conductive layer 110 a_1serving as a source electrode layer over the semiconductor layer 108 andthe insulating layer 106 b; the conductive layer 110 a_2 serving as adrain electrode layer over the semiconductor layer 108 and theinsulating layer 106 b; the insulating layer 112 serving as a protectiveinsulating film over the semiconductor layer 108 and the conductivelayers 110 a_1 and 110 a_2; the insulating layer 116 formed using aphotosensitive resin over the insulating layer 112; the pixel electrodelayer 118 over the insulating layer 116; the liquid crystal layer 166over the pixel electrode layer 118; the conductive layer 164 having afunction of a counter electrode over the liquid crystal layer 166; thespacer 181; the BM 180; the coloring layer 114 having a function of acolor filter; an overcoat layer 182 covering the coloring layer 114; andthe second substrate 162 that is a counter substrate over the conductivelayer 164. In this case, the overcoat layer 182 is in contact with thesecond substrate 162 that is the counter substrate in the opening 136.

As the overcoat layer 182, an acrylic based resin film is used, which isformed by applying an acrylic based resin material with a spin coaterapparatus and then drying the material in an oven apparatus. As for thecoloring layer 114, three colors of red (R), green (G), and blue (B) areused, and green (G), red (R), and blue (B) color filters are formed inthis order in desired positions by light exposure and development. Eachof the red (R), green (G), and blue (B) color filters is formed so as tohave a thickness of 0.8 μm.

Note that the conductive layer 104 a, the insulating layers 106 a and106 b, the semiconductor layer 108, and the conductive layers 110 a_1and 110 a_2 form the transistor 150. The conductive layer 104 b, theinsulating layers 106 a and 106 b, and the conductive layer 110 a_2 formthe capacitor 152. The capacitor 152 has a large area and thus has alarge capacitance for charge storage. Thus, it is possible to retain thepotential of the pixel electrode for a longer time and to apply adriving mode with a reduced refresh rate. Furthermore, a change involtage applied to the liquid crystal layer can be inhibited for a longtime even when the liquid crystal display device is used in the drivingmode with a reduced refresh rate. This makes it possible to preventscreen flickers from being perceived by a user more effectively. Thus,the power consumption can be reduced and the display quality can beimproved.

An effect of reducing the refresh rate will be described here. Note thatthe refresh rate refers to the number of times of image writing persecond and is also called driving frequency. Such high-speed screenswitching that is difficult for the human eye to perceive is consideredas a cause of eye strain.

The eye strain is divided into two categories: nerve strain and musclestrain. The nerve strain is caused by prolonged looking at light emittedfrom a liquid crystal display device or blinking images. This is becausethe brightness stimulates and fatigues the retina and nerve of the eyeand the brain. The muscle strain is caused by overuse of a ciliarymuscle which works for adjusting the focus.

FIG. 27A is a schematic diagram illustrating display of a conventionalliquid crystal display device. As illustrated in FIG. 27A, for thedisplay of the conventional liquid crystal display device, imagerewriting is performed 60 times per second. A prolonged looking at sucha screen might stimulate the retina and nerve of the eye and the brainof a user and lead to eye strain.

In this embodiment, a transistor with an extremely low off-state current(e.g., a transistor using an oxide semiconductor) is used as thetransistor 150 in a pixel portion of a liquid crystal display device. Inaddition, the liquid crystal element has a large-area capacitor. Withthese components, leakage of electrical charges stored in the capacitorcan be inhibited, whereby the luminance of a liquid crystal displaydevice can be kept even at a lower frame frequency.

Thus, for example, the number of times of image writing can be reducedto once every five seconds as shown in FIG. 27B. The same image can beseen for as long as possible and flickers on a screen perceived by auser can be reduced. This makes it possible to reduce stimuli to theretina and nerve of the eye and the brain of a user, resulting in lessnerve strain.

This embodiment makes it possible to provide an eye-friendly liquidcrystal display device.

The refresh operation needs to be performed such that a change of animage caused by the refresh operation is not distinguished by users. Thedisplay device according to this embodiment has little change of animage caused by the refresh operation and can perform favorable display.

The coloring layer 114 formed on the second substrate 162 side isprovided with a plurality of openings 136. The color purity of thecoloring layer 114 can be adjusted by setting the shape or area of theopenings 136 provided in the coloring layer 114. With such a structurein which the coloring layer 114 has the openings 136, a novel displaydevice capable of adjusting color purity can be provided.

The insulating layer 112 is provided with the opening 138. The pixelelectrode layer 118 is connected to the conductive layer 110 a_2 servingas a drain electrode layer of the transistor 150, through the opening138. For the insulating layer 116, a photosensitive resin may be used sothat random projections and depressions are formed. In the case whererandom projections and depressions are formed, the pixel electrode layer118 is a reflective electrode having random projections and depressionsreflecting the random projections and depressions on the surface of theinsulating layer 116. Thus, viewing angle dependence can be improved.

In this embodiment, a highly reflective conductive layer is used as thepixel electrode layer 118 so as to serve as a reflective electrode. Forexample, the highly reflective conductive layer is formed to have asingle-layer structure or a stacked-layer structure including any ofmetals such as aluminum, silver, palladium, and copper or an alloycontaining any of these metals as its main component.

FIG. 23B is a cross-sectional view of a region where the gate line 104and the conductive layer 110 a_2 serving as the source line 110intersect with each other.

In the display device in FIG. 23B, the distance between the firstsubstrate 102 and the second substrate 162 which faces the firstsubstrate 102 is maintained by the spacer 181. In the case wherealignment films are formed, the alignment films may be formed after thespacer is formed by patterning an organic resin film or by forming acolumnar structure using a photosensitive resin.

When the BM 180 is formed as illustrated in FIG. 23B, surface reflectiondue to the gate line 104 or the conductive layer 110 a_2 can besuppressed.

In this manner, the BM 180 is preferably formed in a portion other thanat least a reflective region.

This embodiment can be freely combined with any of the otherembodiments.

Example 1

In this example, a display device of one embodiment of the presentinvention was manufactured and subjected to optical microscopeobservation and cross-sectional observation. Details of samplesmanufactured in this example are described below.

Note that a display device having a structure similar to that of thedisplay device illustrated in FIG. 1. FIGS. 2A to 2C, and FIGS. 3A and3B was manufactured in this example. Thus, portions having functionssimilar to those in FIG. 1, FIGS. 2A to 2C, and FIGS. 3A and 3B aregiven the same reference numerals.

A method for manufacturing the samples which were observed in thisexample will be described below.

As the first substrate 102, a glass substrate was used. Then, theconductive layers 104 a. 104 b, and 104 c were formed over the firstsubstrate 102. A 200-nm-thick tungsten film (W) was formed by asputtering method for the conductive layers 104 a, 104 b, and 104 c.

Then, the insulating layers 106 a and 106 b serving as a gate insulatinglayer were formed over the first substrate 102 and the conductive layers104 a, 104 b, and 104 c. A 400-nm-thick silicon nitride film was formedas the insulating layer 106 a, and a 50-nm-thick silicon oxynitride filmwas formed as the insulating layer 106 b.

Note that the silicon nitride film that is the insulating layer 106 ahas a three-layer structure of a first silicon nitride film, a secondsilicon nitride film, and a third silicon nitride film.

The first silicon nitride film was formed to have a thickness of 50 nmunder the following conditions: silane at a flow rate of 200 sccm,nitrogen at a flow rate of 2000 sccm and an ammonia gas at a flow rateof 100 sccm were supplied to a reaction chamber of a plasma CVDapparatus as a source gas, the pressure in the reaction chamber wascontrolled to 100 Pa, and a power of 2000 W was supplied with the use ofa 27.12 MHz high-frequency power source. The second silicon nitride filmwas formed to have a thickness of 300 nm under the following conditions:silane at a flow rate of 200 sccm, nitrogen at a flow rate of 2000 sccm,and an ammonia gas at a flow rate of 2000 sccm were supplied to thereaction chamber of the plasma CVD apparatus as a source gas, thepressure in the reaction chamber was controlled to 100 Pa, and a powerof 2000 W was supplied with the use of a 27.12 MHz high-frequency powersource. The third silicon nitride film was formed to have a thickness of50 nm under the following conditions: silane at a flow rate of 200 sccmand nitrogen at a flow rate of 5000 sccm were supplied to the reactionchamber of the plasma CVD apparatus as a source gas, the pressure in thereaction chamber was controlled to 100 Pa, and a power of 2000 W wassupplied with the use of a 27.12 MHz high-frequency power source. Notethat the first silicon nitride film, the second silicon nitride film,and the third silicon nitride film were each formed at a substratetemperature of 350° C.

The silicon oxynitride film formed as the insulating layer 106 b wasformed under the following conditions: silane at a flow rate of 20 sccmand dinitrogen monoxide at a flow rate of 3000 sccm were supplied to thereaction chamber of the plasma CVD apparatus as a source gas, thepressure in the reaction chamber was controlled to 40 Pa, and a power of100 W was supplied with the use of a 27.12 MHz high-frequency powersource. Note that the silicon oxynitride film was formed at a substratetemperature of 350° C.

Next, the semiconductor layer 108 was formed so as to overlap with theconductive layer 104 a with the insulating layers 106 a and 106 bprovided therebetween. A 35-nm-thick oxide semiconductor film was formedas the semiconductor layer 108 by a sputtering method.

The oxide semiconductor film was formed under the following conditions:a metal oxide sputtering target of In:Ga:Zn=1:1:1 (atomic ratio) wasused, oxygen at a flow rate of 100 sccm and argon at a flow rate of 100sccm were supplied as a sputtering gas to a reaction chamber of asputtering apparatus, the pressure in the reaction chamber wascontrolled to 0.6 Pa, and an alternating-current power of 2.5 kW wassupplied. Note that the oxide semiconductor film was formed at asubstrate temperature of 170° C.

Next, the opening 132 was formed in a desired position of the insulatinglayers 106 a and 106 b. Note that the opening 132 reaches the conductivelayer 104 b.

The opening 132 was formed using a dry etching apparatus.

Next, a conductive layer was formed over the semiconductor layer 108 andthe insulating layers 106 a and 106 b. As the conductive layer, a400-nm-thick aluminum film was formed over a 50-nm-thick tungsten film,and a 100-nm-thick titanium film was formed over the aluminum film.

Next, a conductive layer 110_1 was formed by removing a region otherthan a desired region of the 100-nm-thick titanium film with a dryetching apparatus. Note that the conductive layer 110_1 is a100-nm-thick titanium film.

Next, the conductive layers 110 a_1, 110 a_2, 110 a_3, 110 a_4, 110 b_1,110 b_2, 110 b_3, and 110 b_4 were formed by processing the 50-nm-thicktungsten film and the 400-nm-thick aluminum film into a desired shapewith a dry etching apparatus. Note that the conductive layers 110 a 1,110 a_2, 10 a_3, and 110 a_4 are each a 50-nm-thick tungsten film. Theconductive layers 110 b_1, 110 b_2, 110 b_3, and 110 b_4 are each a400-nm-thick aluminum film.

The conductive layers 110 a_1 and 110 b_1 serve as a source electrodelayer of a transistor; the conductive layers 110 a_2 and 110 b_2 serveas a drain electrode layer of the transistor; the conductive layers 110a_3 and 110 b_3 serve as a reflective electrode layer; and theconductive layers 110 a_4 and 110 b_4 serve as part of a source line.

Next, the insulating layer 112 was formed so as to cover thesemiconductor layer 108 and the conductive layers 110 b_1, 110 b_2, 110b_3, and 110 c_1.

The insulating layer 112 was formed to have a three-layer structure of afirst oxide insulating film, a second oxide insulating film, and anitride insulating film.

A 50-nm-thick silicon oxynitride film was formed as the first oxideinsulating film. A 400-nm-thick silicon oxynitride film was formed asthe second oxide insulating film. Note that the first oxide insulatingfilm and the second oxide insulating film were successively formed witha plasma CVD apparatus in vacuum without exposure to the air. Since thefirst oxide insulating film and the second oxide insulating film wereformed using the same kind of material, the interface between thesefilms cannot be clearly defined in some cases.

The first oxide insulating film was formed by a plasma CVD method underthe following conditions: silane at a flow rate of 30 sccm anddinitrogen monoxide at a flow rate of 4000 sccm were used as a sourcegas, the pressure in the reaction chamber was 40 Pa, the substratetemperature was 220° C., and a high-frequency power of 150 W wassupplied to parallel-plate electrodes.

The second oxide insulating film was formed by a plasma CVD method underthe following conditions: silane at a flow rate of 160 sccm anddinitrogen monoxide at a flow rate of 4000 sccm were used as a sourcegas, the pressure in the reaction chamber was 200 Pa, the substratetemperature was 220° C., and a high-frequency power of 1500 W wassupplied to the parallel-plate electrodes. Under the above conditions,it is possible to form a silicon oxynitride film containing oxygen at ahigher proportion than oxygen in the stoichiometric composition and fromwhich part of oxygen is released by heating.

Next, heat treatment was performed to release water, nitrogen, hydrogen,and the like from the first oxide insulating film and the second oxideinsulating film and supply part of oxygen contained in the second oxideinsulating film to the oxide semiconductor film used as thesemiconductor layer 108. Here, the heat treatment was performed at 350°C. in a mixed atmosphere of nitrogen and oxygen for one hour.

Then, a 100-nm-thick nitride insulating film was formed over the secondoxide insulating film. A 100-nm-thick silicon nitride film was formed asthe nitride insulating film. The nitride insulating film was formed by aplasma CVD method under the following conditions: silane at a flow rateof 50 sccm, nitrogen at a flow rate of 5000 sccm, and an ammonia gas ata flow rate of 100 sccm were used as a source gas, the pressure in thereaction chamber was 100 Pa, the substrate temperature was 350° C., anda high-frequency power of 1000 W was supplied to the parallel-plateelectrodes.

Next, the coloring layer 114 was formed in a desired region over theinsulating layer 112.

As the coloring layer 114, a photosensitive resin film was formed byapplying a photosensitive resin solution in which a coloring materialwas dispersed, with a spin coater apparatus and then drying the solutionin an oven apparatus. The photosensitive resin film serves as aso-called color filter. Note that in this example, three colors of red(R), green (G), and blue (B) are used, and green (G), red (R), and blue(B) color filters were formed in this order in desired positions bylight exposure and development. Each of the red (R), green (G), and blue(B) color filters was formed so as to have a thickness of 0.8 μm. Thecoloring layer 114 was formed such that the opening 134 and the opening136 were provided for each of the above colors.

Next, the insulating layer 116 having a function of an overcoat wasformed over the insulating layer 112 and the coloring layer 114. Notethat as the insulating layer 116, an acrylic based resin film was formedby applying an acrylic based resin material with a spin coater apparatusand then drying the material in an oven apparatus. The insulating layer116 was formed so as to have a thickness of 2.5 μm. In addition, theinsulating layer 116 was formed such that an opening is provided insidethe opening 134 in the coloring layer 114.

Next, the opening 138 was formed in the insulating layer 112 in aposition overlapping the opening 134. The opening 138 was formed so asto reach the conductive layer 110 c_1. Note that the opening 138 wasformed using a dry etching apparatus.

Next, the pixel electrode layer 118 was formed over the insulating layer116 so as to cover the opening 138. A 100-nm-thick conductive film of anindium oxide-tin oxide-silicon oxide compound (ITO-SiO₂, hereinafterITSO) was formed as the pixel electrode layer 118 by a sputteringmethod. Note that the composition of a target used for forming theconductive film was In₂O₃:SnO₂:SiO₂=85:10:5 [wt %].

Through these steps, elements were formed over the first substrate 102.These samples were subjected to optical microscope observation.

Note that in this example, in order to observe the elements formed overthe first substrate 102, the liquid crystal layer 166, the conductivelayer 164, and the second substrate 162 were not formed over theinsulating layer 116 and the pixel electrode layer 118.

FIGS. 11A to 11C show optical micrographs of the samples manufactured inthis example. Note that the optical micrographs shown in FIGS. 11A to11C are reflected bright-field images.

In addition, FIGS. 11A to 11C are optical micrographs of the sampleswith different shapes and arrangements of the openings 134 and 136 inthe coloring layers 114 as shown in FIGS. 2A to 2C in Embodiment 1. Notethat the shapes and arrangement of the openings 134 and 136 in thecoloring layers 114 were changed by changing the shape of a lightexposure mask.

As shown in FIGS. 11A to 11C, the coloring layer 114 with the openings134 and 136 of any of the shapes was not separated, and these shapes arefound favorable.

In addition, favorable color purity was visually observed from all thesamples in FIGS. 11A to 11C.

FIGS. 11A to 11C each show a top view of roughly three pixels. In eachof FIGS. 11A to 11C, an upper portion is a pixel region in which a red(R) color filter is used as the coloring layer 114; a middle portion isa pixel region in which a green (G) color filter is used as the coloringlayer 114; and a lower portion is a pixel region in which a blue (B)color filter is used as the coloring layer 114.

Note that the proportion of the area of the coloring layer 114 in FIG.11A to the area of the conductive layer 110 b_3 used as a reflectiveelectrode layer in one pixel is 76%. The proportion of the area of thecoloring layer 114 in FIG. 11B to the area of the conductive layer 110b_3 used as a reflective electrode layer in one pixel is 63%. Theproportion of the area of the coloring layer 114 in FIG. 11C to the areaof the conductive layer 110 b_3 used as a reflective electrode layer inone pixel is 41%. Thus, the proportion of the area of the coloring layer114 can be easily changed by changing the shape and arrangement of theopenings 136 in the coloring layer 114.

Next, results of cross-sectional observation of the samples manufacturedin this example are described with reference to FIG. 12 and FIGS. 13Aand 13B. Note that a transmission electron microscope (TEM) was used forthe cross-sectional observation. FIG. 12 shows two TEM images partlyoverlapping with each other. In FIG. 12 and FIGS. 13A and 13B,brightness, contrast, and the like are adjusted to clearly showinterfaces and the like.

Note that FIG. 12 shows a result of a cross section taken alongdashed-dotted line X3-Y3 in FIG. 11A. FIG. 13A shows a result of a crosssection taken along dashed-dotted line X4-Y4 in FIG. 11A. FIG. 13B showsa result of a cross section taken along dashed-dotted line X5-Y5 in FIG.11A.

Note that in FIG. 12 and FIGS. 13A and 13B, Sub. denotes the firstsubstrate 102. GI denotes the insulating layers 106 a and 106 b servingas a gate insulating layer. SiON denotes the silicon oxynitride filmused as the insulating layer 112. SiN denotes the silicon nitride filmused as the insulating layer 112. W denotes the tungsten films used asthe conductive layers 104 a, 104 b, 104 c, 110 a_1, 110 a_2, 110 a_3,and 110 a_4. Al denotes the aluminum films used as the conductive layers110 b_1, 110 b_2, 110 b_3, and 110 b_4. Ti denotes the titanium filmused as the conductive layer 110 c_1. IGZO denotes the oxidesemiconductor film used as the semiconductor layer 108. CF(R) denotesthe coloring layer 114 for red. CF(G) denotes the coloring layer 114 forgreen. CF(B) denotes the coloring layer 114 for blue. OC denotes theacrylic based resin film used as the insulating layer 116 having afunction of an overcoat. ITSO denotes the indium oxide-tin oxide-siliconoxide compound film used as the pixel electrode layer 118. Pt denotes aplatinum coating used as a conductive film for cross-sectionalobservation. C denotes a carbon coating used as a conductive film forcross-sectional observation.

The results shown in the TEM images in FIG. 12 and FIGS. 13A and 13Bconfirm that the display device of this example has a favorablecross-sectional shape. As can be seen from the result shown in the TEMimage in FIG. 13A, in the display device of this example, the colorfilter CF(G) and the color filter CF(R) each used as the coloring layer114 are stacked over the gate line, the source line, or a region wherethe gate line intersects with the source line, which is other than areflective region. In addition, in the display device of this example,the color filter CF(R) and the color filter CF(B) each used as thecoloring layer 114 are stacked over the gate line, the source line, or aregion where the gate line intersects with the source line, which isother than a reflective region.

As can be seen from the result shown in the TEM image in FIG. 13B, thedisplay device of this example has a structure in which the color filterCF(G) used as the coloring layer 114 has an opening, and through theopening, the silicon nitride film (SiN) used as the insulating layer 112is in contact with the acrylic based resin film used as the insulatinglayer 116 serving as an overcoat (OC). Thus, it is confirmed that thedisplay device of this example has a favorable cross-sectional shapewith improved adhesion of the coloring layer 114 and with no filmseparation or the like.

The structure described above in this example can be combined with anyof the structures described in the other embodiments as appropriate.

Example 2

In this example, a display device of one embodiment of the presentinvention was manufactured, a pixel region where an image was displayedwas photographed, and its reflectance was measured. Details of samplesmanufactured in this example are described below.

Note that the display device described in Embodiment 5 and illustratedin FIG. 21, FIGS. 22A and 22B, and FIGS. 23A and 23B was manufactured inthis example. In addition, a display device in which all the coloringlayers in R, G, and B pixels had the same shape was manufactured. Thedisplay device in this example is the same as the display deviceillustrated in FIG. 1, FIGS. 2A to 2C, and FIGS. 3A and 3B, except thatopenings in coloring layers for different colors have partly varyingshapes, the coloring layers are formed over a counter substrate, and apixel electrode is used as a reflective electrode, for example. Thus,portions having functions similar to those in FIG. 1, FIGS. 2A to 2C,and FIGS. 3A and 3B are given the same reference numerals.

Two types of display panels which are the manufactured samples weresubjected to reflectance measurement using a measurement apparatus (anLCD evaluation apparatus (product name: LCD-7200)) such that a detectorwas positioned over the center of the display panel so as to beperpendicular to the display panel surface and the center of the panelwas irradiated with light from a light source at an angle in the rangefrom 15° to 70°, as illustrated in FIG. 24A. FIG. 24B shows the results.

The upper curve in FIG. 24B represents data obtained from the displaydevice described in Embodiment 5, and the lower curve represents dataobtained from the display device in which the coloring layers in the R.G, and B pixels have the same shape that is illustrated in FIG. 22A.

FIG. 25A shows a photograph of display by the display device describedin Embodiment 5.

FIG. 25B shows a table of characteristics of the two types of displaydevices. In FIG. 25B, the display device described in Embodiment 5 isreferred to as high reflective LCD because of its high reflectance, andthe other display device is referred to as high color gamut LCD.

These panels can further be provided with a touch panel so as to be adisplay device capable of touch input. FIG. 26 is a schematic diagram ofa configuration example of a display device including a touch panel. Adisplay device illustrated in FIG. 26 includes the pixel electrodelayers 118 over the substrate 102; the coloring layers 114 overlappingwith the pixel electrode layers 118; the BM 180 between the coloringlayers 114 for different colors; the substrate 162; a liquid crystalbetween the substrate 102 and the substrate 162; an optical film 183over the substrate 162; a touch panel 184; and a polarizing film 185.Note that transistors electrically connected to the pixel electrodelayers 118 formed over the substrate 102 are not illustrated in FIG. 26.

Note that the data in FIG. 24B and FIGS. 25A and 25B were obtainedbefore a touch panel is provided.

These data indicate that a reflective liquid crystal display devicecapable of high-resolution display can be obtained.

Furthermore, these display panels include capacitors with a largecapacitance. Thus, it is possible to retain the potential of the pixelelectrode for a longer time and to apply a driving mode with a reducedrefresh rate. Moreover, a change in voltage applied to the liquidcrystal layer can be inhibited for a long time even when the liquidcrystal display device is used in the driving mode with a reducedrefresh rate. This makes it possible to prevent screen flickers frombeing perceived by a user more effectively. Thus, the power consumptioncan be reduced and the display quality can be improved.

FIG. 28 shows results of measuring changes in images caused by a refreshoperation in the display device of this example. As shown in FIG. 28,little change is caused in images by the refresh operation in any ofwhite display, gray display, and black display.

The display device of this example can be used in a driving mode with areduced refresh rate of 1 Hz or less and can be an eye-friendlyreflective liquid crystal display device. The display device of thisexample can also be a low-power-consumption reflective liquid crystaldisplay device.

This application is based on Japanese Patent Application serial no.2013-216904 filed with Japan Patent Office on Oct. 18, 2013 and JapanesePatent Application serial no. 2014-005432 filed with Japan Patent Officeon Jan. 15, 2014, the entire contents of which are hereby incorporatedby reference.

What is claimed is:
 1. A display device comprising: a first substrate; atransistor over the first substrate; an electrode layer electricallyconnected to the transistor; a first insulating layer over the electrodelayer; a pixel electrode layer over the first insulating layer; a secondinsulating layer over the pixel electrode layer; a first coloring layerover the second insulating layer, the first coloring layer overlappingwith the electrode layer and the pixel electrode layer; and a secondsubstrate over the first coloring layer, wherein the first coloringlayer includes a first opening, and wherein the second insulating layeris in contact with the second substrate in the first opening.
 2. Thedisplay device according to claim 1 further comprising a second coloringlayer, wherein the second coloring layer includes a second opening, andwherein an upper surface shape of the second opening is different froman upper surface shape of the first opening.
 3. The display deviceaccording to claim 1, wherein the pixel electrode layer is a reflectiveelectrode layer.
 4. The display device according to claim 1, wherein thetransistor comprises a gate electrode layer, a gate insulating layer anda semiconductor layer, the gate electrode layer overlapping with thesemiconductor layer, wherein the gate insulating layer is providedbetween the gate electrode layer and the semiconductor layer, andwherein a source electrode layer and a drain electrode layer are incontact with the gate insulating layer and the semiconductor layer. 5.The display device according to claim 4, wherein the semiconductor layercomprises an oxide semiconductor.
 6. The display device according toclaim 5, wherein the oxide semiconductor includes an oxide representedby an In-M-Zn oxide containing at least indium (In), zinc (Zn), and M,and wherein M represents Al, Ga, Ge, Y, Zr, Sn, La, Ce, or Hf.
 7. Anelectronic device comprising the display device according to claim 1.